





: 






UNITED STATES OF AMERICA. 





EXPLOSIONS 



tisXlJy J-L 



OF 



STEAM BOILERS: 



HOW THEY ARE CAUSED, AND HOW 
THEY MAY BE PREVENTED. 



J 
Br J. R. ROBINSON, 



STEAM-ENGINEER. 




BOSTON: 
LITTLE, BROWN, AND COMPANY. 

1870. 






Entered according to Act of Congress, in the year 1870, by 

J. R. ROBINSON, 

In the Office of the Librarian of Congress, at Washington. 



(,-pH 



ft 



CAMBRIDGE I 
PRESS OF JOHN WILSON AND SON. 



CONTENTS. 



PAGE 

Explosions caused by Low Water 11 

„ Overpressure 20 

„ Defects in Materials, &c. ... 28 

„ Scale or Sediment 29 

„ Kepulsion of the Water .... 81 

„ Overheating of the Water ... 61 

How Explosions caused by Low Water may be prevented 76 

„ „ „ — „ Overpressure „ „ 82 

„ „ „ „ Defective Materials, &c., may 

be prevented 83 

How Explosions caused by Scale and Sediment may 

be Prevented „ 89 

How Explosions caused by Kepulsion of the Water 

may be Prevented 91 

How Explosions caused by Overheating of the Water 

may be Prevented 94 



PREFACE. 



While it is true that the condition of many boilers now 
in use is such that it is a matter of surprise that so few 
boiler explosions occur, having their origin in excessive press- 
ure, overheating of the surfaces above the water, in defects 
of materials of construction, and in the presence of scale 
and sediment, it is also true that there have been so many 
explosions not attributable to either of these causes, as to 
point unmistakably to the existence and operation of a power 
not indicated by the pressure gauge. Many theories have 
been advanced to account for these explosions, but without 
such a clearing up of the mystery as has resulted in the 
general adoption of means for their prevention. Many at- 
tempts have been made to construct boilers of parts so small 
that the explosion of one of them will not lead to very seri- 
ous results ; but such boilers are so deficient in area of water- 
level, and in steam room, and there are such difficulties in 
the way of maintaining the water at the same level in the 
different sections — with the necessary exposure of the sur- 
faces in order to vaporize the water thrown up mechanically 
mixed with the steam — that there must be so much surface 
exposed to the action of the fire above the water, as to cause 
a dangerous superheating of the steam when but little water 
is thrown up, or the quantity of water so thrown up will at 
times be so great as to unfit the boiler for use. And there 
are comparatively few waters so free from impurities, that 
such boilers will not have their surfaces so coated with non- 



VI PREFACE. 

conducting substances as to cause a rapid loss of their power. 
So it is found that the remedy for boiler explosions does not 
lie in this direction, but rather in such an improvement in 
the construction, and in the employment of such means for 
the safety of boilers having the necessary area of water- 
level, steam room, provision for the circulation of the water, 
and for reaching all the surfaces for the removal of scale 
and sediment, that the water level can be maintained with- 
out serious fluctuations ; and that so little water will be 
thrown up mechanically mixed with the steam, that the ac- 
tion of the heat can be confined entirely to the parts of the 
boiler always covered by water. And notwithstanding the 
desirableness of avoiding the use of very large shells for 
high pressures because of the objections to the use of very 
thick plates, it is undoubtedly better to use iron of such a 
quality that the requisite strength can be got in large shells, 
than to resort to the use of sets or " batteries " of boilers 
of smaller diameter fed together, because of the dangers 
connected with the variation of the water-level in the differ- 
ent boilers in a set or " battery." Probably a large propor- 
tion of all the explosions on our western waters, have had 
their origin in this cause. 

It is my aim to set forth in the following pages, in as few 
words- as possible, — with the necessary citation of acknowl- 
edged authorities, and reports of cases in the several classes 
of explosions, — the causes of the explosion of steam-boilers, 
and the means to be used for their prevention, that all interested 
in these matters may be in possession of the important facts 
in relation to them. I do this with the feeling that a report 
of some of the more important facts observed by me during 
my experience and experiments, will be of value, inasmuch 
as they throw light upon the classes of explosion hitherto 
involved in so much mystery ; and especially that a report 



PREFACE. Vll 

of the wonderful manifestations of the power of the repul- 
sive action of heat upon water, and of the explosive force or 1 
the sudden vaporization of water on the bottom of a steam- 
boiler, caused by the reduction of the temperature of the 
surfaces, as witnessed by me during recent experiments for 
determining the strength of certain metals when exposed to 
pressure and to the action of the heat in the bottom of a 
steam-boiler, will not only prove of interest, as throwing 
light upon the cause of one class of these explosions, but 
will be of great value as pointing to the means by which 
they may be prevented. These experiments show, in 
relation to the repulsive power of heat, as will be seen in 
connection with the class of explosions caused by the sud- 
den vaporization of water on the bottom of a boiler, that it 
is a power always active during the vaporization of water 
under pressure, and ever ready to assert itself by driving the 
water from the surfaces exposed to the action of heat ; that 
pressure does not appear to change the temperature of maxi- 
mum vaporization ; and that, while pressure alone does not 
change the temperature of perfect repulsion, the combined 
action of pressure, and of a forcible circulation of the water 
against the surfaces exposed to the heat, does so far over- 
come the power of the repulsive action, that, so long as the 
circulation is kept up, the temperature of perfect repulsion 
is practically raised. These experiments also show how a 
strong steam boiler may be caused to explode at, or below, 
the ordinary working pressure, without a sign of trouble 
with the water noticeable at the surface up to the time of the 
explosion, and without an elevation of the temperature of 
the boiler that it would be possible to detect by the most 
careful examination afterwards. 

J. R. EOBINSON. 

Boston, July 29, 1870. 



J 



STEAM-BOILER EXPLOSIONS. 



Before considering the subject of Steam-Boiler Ex- 
plosions, it is to be remarked, that the number of 
boilers so injured from various causes, as to require 
repairs, is vastly greater than the number of those 
that explode. For instance, a great many cylindrical 
boilers, having the fire under the shell, and the feed- 
water introduced on the bottom, have been broken 
on the bottom by the contraction of the iron in this 
way. The feed-water, especially when introduced at 
a low temperature, and fast, cools off the bottom of 
the boiler ; but the ends of the outside course, at the 
" roundabout" seams, do not have their temperature 
reduced so fast as the other parts of the plate, because 
the ends of the inside course, and the non-conduct- 
ing sediment between the plates, especially when 
the outside course is too large, come between them 
and the water. It will be seen that the temperature 
of this part of the plate, with an intense fire, is always 
much above that of the plate where there is but one 
thickness of iron ; so that there may be, in feeding, 
a difference of temperature of 200° or more in the 
same plate, and within a very short distance, so that 

2 



10 STEAM-BOILER EXPLOSIONS. 

every time the feed is introduced, the iron in the out- 
side course, just at the end of the inside course, is 
subjected to a strain, while, at the same time the reduc- 
tion of the temperature of the bottom of the boiler 
brings a strain in the opposite direction, till in time the 
strength of the iron is so reduced that it gives way at a 
time, when, perhaps, the temperature of the feed-water 
is lower than usual, or its quantity is greater, or the 
fire is a little lower ; the pressure of the steam upon the 
boiler having nothing directly to do with the breaking, 
excepting as a higher pressure, with its higher tem- 
perature, would make morq difference in temperature 
between the top and bottom of the boiler. In some 
instances these breakages are so large as to amount 
to over one-sixth of the circumference of the boiler, 
without leading directly to any other ill effect than 
letting the water out of the boiler. 

Many more boilers are burned so as to need repairs, 
than are thrown out of their places, because of an ac- 
cumulation of scale or sediment over or around their 
fires. 

Many " drop flue " boilers have been broken without 
leading to an explosion, by the strain, together with 
the corrosion, induced in all cases — so far as I am 
aware, unless in cases where the iron is protected by 
scale — where steam is made in the upper part of a 
boiler, while the water in the bottom is at a low and 
varying temperature. Several boilers of this class that 
came under my observation, — boilers about twenty- 
five feet long, five feet in diameter, and running under 
a steam pressure of sixty pounds per square inch, fed 



STEAM-BOILER EXPLOSIONS. 11 

on the bottom with water at times as low as 40° P., 
and with so little heat left in the gases when they 
came to the bottom of the shell, that the water on the 
bottom was hardly ever up to the temperature due 
the pressure, — were corroded very fast at and near 
the bottom, and had many leaks and breakages, but 
no explosion. 

Many boilers have been broken, where explosion 
has not resulted, by the strain thrown upon the iron, 
because of the exposure of a part of the shell, not 
covered by the water, to the action of the heated 
gases. And many boilers have been caused to leak, 
without leading to explosion, because of overheating 
resulting from low water ; the overheating causing the 
boiler to leak so much, perhaps, as to prevent the ex- 
plosion, before the tensile strength of the iron was so 
reduced., by the elevation of temperature, as to lead 
to the rupture of the boiler by pressure. 

Many boilers are injured, so as to need repairs, by a 
repulsion of the water from their surfaces exposed to 
the fire (below the surface of the water), when, either 
because of the presence of a scale or coating that is not 
removed or changed by the elevation of temperature, 
or when, from some other cause, the reduction of the 
temperature of the overheated surfaces is not so rapid 
as to lead to explosion. 

And this leads to the consideration of the matter of 
explosions caused by low water. While it is undoubt- 
edly true, that an explosion not preceded by a sudden 
increase of pressure will result from low water, when- 
ever the strength of the iron of the boiler, by its 



12 STEAM-BOTLER EXPLOSIONS. 

elevation of temperature, is reduced below the point 
required to withstand the steam pressure, yet, in view 
of the fact demonstrated by the experiments of the 
Committee of the Franklin Institute,* and by the 
experiments of Mr. Fairbairn,f that the tensile strength 
of most boiler iron is increased by an elevation of 
temperature, so that it is greater at about 400° F. than 
at any temperature below that, and that its tensile 
strength is not seriously reduced at (>00° F. (in fact, 
some iron proving stronger at 600° than at any lower 
temperature), and that thus, for some time before the 
reduction of the tensile strength of the iron, the boiler 
is in a condition to vaporize suddenly a greater or less 
quantity of water, probably most explosions from low 
water have been preceded by a sudden elevation of 
pressure, not necessarily great ; but so sudden as to 
rupture the boiler, and to let so much steam escape 
that the reduction of pressure shall cause the water 
in the boiler to be thrown, in the act of giving off its 
steam, with such force as to shatter the boiler. That 
the violence of boiler explosions is due very largely 
to the percussive action of the steam and water con- 
tained in them at the time of rupture, there can be 
no doubt. For a very clear setting forth of this action, 



* For a full report of the very Interesting experiments of this Com- 
mittee, (Hi the causes of boiler explosions, and for several able papers 
relating to the subject, see Volumes 17, IS, 19, and 20, New Series, 
" Journal of the Franklin Institute." 

1 For a full report of the experiments of Mr. Fairhairn, which arc 
of great value to all interested in the strength of boilers, see " Useful 
Information for Engineers," London: Longman, Green, Longman, 
& Roberts. First Series, 1850 ; and Second Series, I860. 



STEAM-BOILER EXPLOSIONS. 13 

see " Steam Boiler Explosions," by Zerah Colburn ; 
London: John Weale, 1860. Mr. Colburn says: 
" But the momentum of the combined steam and 
water discharged, as Mr. Clark has suggested in his 
communication already referred to, would probably 
be sufficient to overcome the resistance of the material 
of the boiler, and to rend it open, not only along seams 
of rivets, but, as is often the case, through solid iron 
of the strongest quality." 

Mr. D. K. Clark, in the communication to which 
Mr. Colburn refers, and which is given by him in full, 
says : " And I beg leave to suggest, that the sudden 
dispersion and projection of the water in the boiler 
against the bounding surfaces of the boiler is the great 
cause of the violence of the results ; the dispersion 
being caused by the momentary generation of steam 
throughout the mass of the water, and its efforts to 
escape. It carries the water before it, and the com- 
bined momentum of the steam and water carries them, 
like shot, through and amongst the bounding surfaces, 
and deforms or shatters them in a manner not to be 
accounted for by simple overpressure, or by the simple 
momentum of steam." Mr. Colburn, in giving a sum- 
mary of this action, says : " The distinct and consecutive 
operations into which a boiler explosion, although prac- 
tically instantaneous, may probably be resolved, are 
these : — 

" First. The rupture, under hardly, if any, more 
than the ordinary working pressure, of a defective 
portion of the shell of the boiler, — a portion not 
much, if at all, below the water-line. 



14 STEAM-BOILER EXPLOSIONS. 

" Second. The escape of the free steam from the 
steam-chamber, and the consequent removal of a con- 
siderable part of the pressure upon the water, before 
its contained heat can overcome its inertia, and permit 
the disengagement of additional steam. 

" Third. The projection of steam, combined — as 
it necessarily must be — with the water, with great 
velocity, and through a greater or less space, upon the 
upper sides of the shell of the boiler, which is thus 
forced completely open, and perhaps broken in pieces. 

" Fourth. The sudden disengagement of a large 
quantity of steam from the heated water, now no 
longer confined within the boiler, and the consequent 
projection of the already separated parts of the boiler 
to a greater or less distance." 

To return to the consideration of the subject of the 
sudden elevation of pressure when the water is low, — 
it is to be borne in mind that at such a time all the 
parts of the boiler above the water, together with 
the steam contained in it, is at a temperature above 
that due the pressure within the boiler; so that, in 
case any of the water in the boiler, having a temper- 
ature due the pressure, be thrown up, all the heat 
imparted to it is expended in vaporizing the water, 
and as a consequence in an elevation of pressure. 
That this rise of pressure may be so violent as to lead 
to the rupture of the boiler was pointed out by Mr. 
Jacob Perkins, several years ago. Mr. Perkins, who 
had had great experience in the vise of steam of high 
pressure, says, in speaking of the causes of boiler 
explosions (see " Journal of Franklin Institute," 



STEAM-BOILER EXPLOSIONS. 15 

New Series, Vol. 17, p. 371) : " The second cause 
of explosion, which I some years since accidentally 
discovered and published, — and which explanation has 
since been experimentally proved to be correct by the 
celebrated French philosopher, M. Arago, — arises from 
the water getting too low in the boiler. The fire then 
impinging on that part of the boiler which is above the 
water causes the heat to be taken up by the steam, 
which rises by its superior levity to the top of the 
boiler, causing it sometimes to become red-hot, and 
so elevating the steam to a much higher temperature 
than its pressure would indicate. Now when the 
boiler is in this state, and the safety-valve suddenly 
raised, the water will be relieved from steam pressure 
and rush up amongst the surcharged steam, which 
thus receives its proper dose of water ; at the same 
time, that part of the boiler which has been raised in 
temperature, giving off its heat to the water so elevated, 
steam is generated in an instant of such force as no 
boiler hitherto made can resist. This kind of explo- 
sion has of late been very frequent and disastrous, 
particularly in America." 

The correctness of this theory of Mr. Perkins 
has been questioned, particularly in relation to the 
effect of superheated steam, because of the fact of its 
low specific heat ; but it is to be borne in mind that the 
action of the superheated steam upon the water thrown 
up mechanically mixed with the steam, while it does 
not vaporize a large quantity of it, acts so rapidly, — so 
explosively, so to speak, — as to so completely disperse 
the remainder over every part of the overheated 



16 STEAM-BOILER EXPLOSIONS. 

surface as that the rapidity of the elevation of pressure 
shall be very much greater than it would be but for 
the presence of superheated steam ; and also that the 
boiler at such a time, at and near the water-level, is 
under such a strain from unequal expansion, that the 
shock produced by the sudden vaporization of even a 
small quantity of water might break it, even without 
such an overheating above the water-line as would 
seriously reduce the tensile strength of the iron. 

The experiments of the Committee of the Franklin 
Institute are conclusive, as to the fact of the sudden 
elevation of pressure when water is thrown into an 
overheated boiler. In relation to this matter, the 
Committee say : " It has been supposed that because 
the metal of a boiler was heated above the temper- 
ature at which the metal would produce steam most 
rapidly, it was impossible to account for the formation 
of quantities of highly elastic steam by such a cause. 
The Committee determined to make the fact of the 
production of high steam by intensely heated metals 
the subject of a direct experiment, and under circum- 
stances as nearly similar as possible to those which 
may occur in a boiler of which some parts, as the sides 
or interior flues, may become unduly heated when not 
in contact with water." 

In these experiments the temperature of the water 
injected was 70°. The pressure on the boiler at the 
instant of the commencement of each experiment was 
one atmosphere, the temperature of the steam within 
the boiler, as shown by a thermometer near the bottom, 
varying from 306° to 448°. Eegarding the working 



STEAM-BOILER EXPLOSIONS. 17 

of the injected water, under the repulsive action of the 
overheated boiler, the Committee, after explaining how 
the water was injected, — at the back end of the boiler, 
— and that its course " could be distinctly marked after 
the bottom of the boiler had been heated to redness, 
and was examined through the glass window," say : 
" The force of the pump carried it to the front end, 
nearly ; the boiler being slightly inclined to the back 
end, the water slid back in one or more dark masses, 
moving down the central line, or diverted up the sides, 
greatly agitated, and frequently changing its shape. 
The water generally disappeared at the back end, 
though parts were retained by accidental spots of sedi- 
ment, and disappeared upon them." In every instance 
the injection of water was followed by a rapid rise in 
pressure ; and at last, when the temperature of the 
steam near the bottom of the boiler was 448°, and 
when the metal of the bottom of the boiler was red, 
the injection of ten fluid ounces of water at 70° was 
followed by a sudden rise of pressure to twelve atmos- 
pheres, and by the shattering of one of the plate-glass 
windows of the boiler. The Committee say: " In the 
last experiment the glass window, of the fire end of 
the boiler, blew out with a quick, sharp report, as loud 
as that of a musket; the fragments of glass from a 
hole in the centre of the plate were projected through 
a window, about three feet from the boiler, and could 
not be found. The number of twelve atmospheres is 
placed opposite to this experiment, as being an approxi- 
mate result. In the act of observing the gauge, the 
glass burst, and the mercury at once fell : the number 



18 



STEAM-BOILER EXPLOSIONS. 



of inches at which the mercury had certainly risen, and 
above which it was, — by an undetermined quantity, 
not, however, very considerable, — was noted ; and from 
this the pressure given in the table is calculated. Here 
explosive steam was generated by the injection of water 
upon red-hot iron, and in a time not exceeding one or 
two minutes at the most, the interval between the last 
stroke of the pump and the explosion not having been 
sufficient to note the height of the gauge." 

In relation to the fact that there was not water 
enough injected in the experiments to give the greatest 
rise of pressure, the Committee say : " By comparing 
the temperature of the steam in these experiments, 
with its observed pressure, it will be seen that not in 
one of them was water enough injected to give the 
steam a density even approaching that corresponding 
to its temperature: for example, 336° F." — the tem- 
perature of the steam, as shown by a thermometer 
near the top of the boiler, after the injection of the 
water — "should give a pressure of 7£ atmospheres, 
instead of 3*3 the observed pressure ; 338° should 
give more than 14 atmospheres (Arago and Dulong), 
instead of 8-2 the observed pressure; and 448° about 
27^ atmospheres, instead of 10. The violence of the 
effect was not, therefore, carried so far as it might have 
been to produce the greatest effect ; and yet within two 
minutes the pressure was raised from one to twelve 
atmospheres." In relation to the fact that the tempera- 
ture of their boiler was too high for the most rapid vap- 
orization, in these experiments, the Committee say: 
" Though it has been shown that water thrown upon 



STEAM-BOILER EXPLOSIONS. 19 

red-hot metal is adequate to produce explosive steam, 
even when it does not cool the metal down to the tem- 
perature of most rapid vaporization, it is not the less 
true that metal more than two hundred degrees below 
a red heat, in the dark, is in the condition to produce 
even a more rapid vaporization of the water thrown 
upon it, than at a red heat." 

It will be noticed that the conditions in these experi- 
ments are unlike those in a steam boiler in which 
the water is low, and water is thrown up by a sud- 
den reduction of pressure, in this : that the water, by 
the repulsive action of the overheated iron, is thrown 
up more in masses, and consequently that it would 
not be brought into such an intimate admixture with 
the superheated steam, nor thrown so completely over 
all the overheated metal of the boiler, as in that case ; 
and that the effect of the superheated steam would be 
less than in a case where its pressure was greater, — 
the temperature being the same; — so there is every 
reason to suppose that the elevation of pressure would 
be more rapid still, in case of low water and the same 
overheating above the water, than was the case in these 
experiments. 

In order to test the question of the action of the 
superheated steam alone in raising the pressure, in 
such a case, and also with a view to test the correctness 
of that part of the theory of Mr. Perkins, the Com- 
mittee made some experiments, that appeared to de- 
monstrate that no rise of pressure would be caused by 
injecting water into superheated steam, and that thus 
the correctness of the theory of Mr. Perkins was dis- 
proved ; but the conditions in the experiments were 



20 STEAM-BOILER EXPLOSIONS. 

unlike those in the case supposed by Mr. Perkins in 
this : that the steam was not superheated from below, 
l?ut by a fire on the top of the boiler ; * that the water 
injected was not at a temperature due the pressure 
within the boiler, but below 212° ; and that in injecting 
the water, it was not brought into such contact with the 
superheated steam as to affect it, or to be affected by 
it ; for the report of these experiments shows that, in 
every instance, the thermometer in the steam in the 
top of the boiler, stood as high, or higher, after as be- 
fore the injection of the water. It may be difficult 
to decide just where the line is to be drawn between 
the effect of the superheated steam and of the over- 
heated metal, in producing a dangerous rise of press- 
ure in an overheated boiler, in which there is a 
throwing up of the water by a sudden reduction of 
pressure, caused either by the raising of a safety- 
valve, the starting of an engine, or by the sudden 
opening of any valve connected with it; but of the 
fact of the rise in pressure, and that it has ruptured, 
and so caused the explosion of many boilers, there 
can be no doubt. 

Explosions of boilers from a steady increase of press- 
ure, without overheating, occur whenever the pressure 

* In relation to this, Mr. Perkins, in a communication to the "Jour- 
nal of the Franklin Institute/' Vol. 20, p. 34, after stating how he got 
the results indicated in his theory, says : "If I had made the fire on 
the top of the boiler, as the Committee of the Franklin Institute did in 
their experiments, I should have made the same mistake ; and instead 
of surcharging the mass of the steam, I should only have surcharged 
a small film next the heated metal, and have left the rest perfectly sat- 
urated with water, and quite unfit for receiving a part of that fluid, 
which would only serve to lower the temperature and pressure, which 
was shown in their experiments." 



STEAM-BOILER EXPLOSIONS. 21 

of the steam is increased beyond the strength of the 
boiler ; and the rupture, or break, will commence at the 
weakest part of the boiler. The violence of the ex- 
plosion will depend upon the pressure at the time, and 
upon the point, as regards the water-level, at which 
the boiler yields. 

Such explosions, when they occur in cases of prop- 
erly constructed boilers, can only be produced by press- 
ures very much above the ordinary working pressures, 
and may be produced by an accidental or a wilful over- 
loading of the safety-valve ; by the adhesion of the 
valve to its seat ; by the closing of a stop-valve between 
the safety-valve and the boiler ; by the failure of the 
valve because of the working loose of its seat, so that 
when the valve rises enough to make a strong upward 
current of steam, the seat is taken up by it, and the 
opening closed ; or by the closing up of the hole in the 
seat upon the spindle or wings of the valve, because 
of the greater expansion of the seat than of the case, 
with such force as to lead to a great over-pressure. I 
have seen several instances of such contraction, where 
the valve was held so securely as to withstand a press- 
ure very much greater than that due the load on 
the valve. In one instance, that of a six-inch valve, 
which had been in use for some years, and perfectly 
free, which was taken out of the case when there was 
a little steam floating up through the seat, with a 
strong current of cold air past the case, the tempera- 
ture of the seat was so much above that of the case, 
as to close up the hole in the seat to such an extent 
that the spindle would not enter it without a consider- 
able reduction of its size. 



22 STEAM-BOILER EXPLOSIONS. 

Mr. Fairbairn supposes that a large proportion of 
all the explosions that occur, are produced by a con- 
tinuous increase of pressure without the means of 
escape. He says (see his " Useful Information for 
Engineers ") : " So many accidents have occurred from 
this cause, — the defective state of the safety-valves, 
— that I must request attention while I enumerate a 
few of the most prominent cases that have come before 
me. In the year 1845 a tremendous explosion took 
place in a cotton-mill in Bolton. The boilers, three in 
number, were situated under the mill ; and from the 
unequal capacity and imperfect state of the safety- 
valves (as they were probably fast), a terrific explo- 
sion of the weakest boiler took place, which tore up 
the plates along the bottom, and, the steam having no 
outlet at the top, not only burst out the end next the 
furnace, demolishing the building in that direction, 
but tore up the top on the opposite side, and the boiler 
was projected upwards in an oblique direction, carrying 
the floors, walls, and every other obstacle, before it ; 
ultimately, it lodged itself across the railway, at some 
distance from the building. Looking at the disastrous 
consequences of this accident, and the number of per- 
sons (from sixteen to eighteen) who lost their lives on 
the occasion, it became a subject of deep interest to 
the community that a close investigation should be > 
immediately instituted ; and a recommendation followed, 
that every precaution should be used in the construc- 
tion as well as the management of boilers. 

" The next fatal occurrence on record in this district 
was at Ashton-under-Lyne, where a boiler exploded 



STEAM-BOILER EXPLOSIONS. 23 

under similar circumstances, namely, from excessive 
interior pressure, where four or five lives were lost; 
and again, at Hyde, a similar accident occurred from 
the same cause, which was afterwards traced to the 
insane act of the stoker or engineer, who prevented 
all means for the steam to escape by tying down the 
safety-valve." 

Mr. Fairbairn gives the facts in relation to the " ter- 
rific explosion at Rochdale, accompanied with great loss 
of life," of a boiler, the ordinary working pressure of 
which was fifty pounds to sixty pounds per square inch. 
He says : " With the exception of some parts of the 
boiler and fragmental parts of the machinery, which 
had been removed when searching for the bodies of 
those killed, I found the buildings, steam-engine, 
boiler, and machinery, a heap of ruins. The boiler 
was torn into eight or ten pieces ; one portion (the 
cylindrical part) flattened and embedded at a consid- 
erable depth in the rubbish, and the two hemispherical 
ends burst asunder and driven in opposite directions 
to a distance of thirty to thirty-five feet from the 
original seating of the boiler. Other parts of the 
cylinder and ends were projected over the buildings 
across Gas-house Lane, and lodged in a field at a 
distance of ninety yards from the point of projection. 
To one of these parts was attached the 2 rf safety-valve, 
which was torn from the boiler by the force of the 
explosion, and carried, along with its seating, over a 
rising ground to a distance of nearly two hundred and 
fifty yards. The other portion of the cylindrical part 
of the boiler was found on the opposite side in the bed 



24 STEAM-BOILER EXPLOSIONS. 

of the river ; and the hemispherical end of this part 
(furthest from the furnace) was rent in two, and 
thrown on each side to a distance of thirty or thirty- 
five feet. These two pieces had evidently come in 
contact with the chimney, razed it to the ground, 
and finally lodged themselves in the margin of the 
river." 

After a careful examination of the parts of the 
exploded boiler, Mr. Fairbairn says, in relation to its 
strength : " In the question before us I find the 
boiler with hemispherical ends, 18 feet long, 5 feet 
diameter, and composed of plates -^ of an inch thick, 
to be equal in its powers of resistance to a pressure 
of three hundred and thirty-five pounds on the square 
inch ; but finding one of the plates under -^ in thick- 
ness, I have reduced its power to three hundred 
pounds, which I consider the force at which it would 
burst." 

Mr. Fairbairn also gives the facts in relation to the 
locomotive " Irk," " which in February, 1845, blew up 
and killed the driver, stoker, and another person who 
was standing near the spot at the time. A great dif- 
ference of opinion as to the cause of this accident was 
prevalent in the minds of those who witnessed the 
explosion, some attributing it to a crack in the copper 
fire-box, and others to the weakness of the stays over 
the top. Neither of these opinions was, however, 
correct, as it was afterwards demonstrated that the 
material was not only entirely free from cracks and 
flaws, but the stays were proved sufficient to resist a 
pressure of one hundred and fifty to two hundred 



STEAM-BOILER EXPLOSIONS. 25 

pounds on the square inch. The true cause was after- 
wards ascertained to arise from the fastening down of 
the safety-valve of the engine (an active fire being in 
operation under the boiler at the time), which was 
under the shed, with the steam up, ready to start with 
the early morning train. The effect of this was the 
forcing down of the top of the copper fire-box upon 
the blazing embers of the furnace, which, acting upon 
the principle of the rocket, elevated the boiler and 
engine of twenty tons weight to a height of thirty 
feet, which, in its ascent, made a summersault in the 
air, passed through the roof of the shed, and ultimate- 
ly landed at a distance of sixty yards from its original 
position." 

Mr. Fairbairn also reports the case of the explosion 
of a locomotive on the Eastern Division of the London 
and North-Western Railway, and in connection with it 
a full account of the very interesting experiments in 
relation to its probable strength. In respect to the 
appearance of the boiler after the explosion, he says : 
" I found one side of the fire-box completely severed 
from the body of the boiler, the interior copper box 
forced inwards upon the furnace ; and, with the excep- 
tion of the cylindrical shell which covers the tubes, the 
whole of the engine was a complete wreck." This engine 
was about thirteen years old, had run 104,723 miles, 
and had been worked under a pressure of sixty pounds 
per square inch. The inside fire-box (copper), which 
was originally T ^ of an inch thick, had been reduced by 
wear so that it was but little over f of an inch, and was 
" perfectly free from flaw or patch." The outer shell 

3 



26 STEAM-BOILER EXPLOSIONS. 

was also good, and " nearly of the original thickness." 
The screw stays were originally ±± of an inch in diame- 
ter, but were reduced from oxidation. The report 
says : " With the exception of one stay, which was on 
the top row, the one most reduced from oxidation was 
half an inch in diameter." They were placed 5-| 
inches by 5 inches from centre to centre. 

Owing to a difference of opinion regarding the 
strength of the boiler, it appearing to be improbable 
that the steam pressure could have increased from 
sixty pounds (the pressure at which it was blowing off 
when the safety-valve was screwed down) to a pressure 
so great as would cause the boiler to.yield, taking Mr. 
Fairbairn's estimate of its strength to be correct, in 
the time (twenty-five minutes) between the screwing 
down of the valve and the explosion, experiments were 
made to test the matter. Regarding the strength of 
the sides of the fire-box, Mr. Fairbairn says : " Tak- 
ing into account the tensile strength of the stays — in 
their corroded state — of the side of the fire-box, which 
to appearance was the first to give way, I find that a 
force of three hundred and eighty pounds upon the 
square inch would be required to effect rupture." . . . 
" Assuming, therefore, that the ends of the screws 
were riveted, and sound in other respects, we may rea- 
sonably conclude that a strain of not less than four 
hundred and fifty to five hundred pounds upon the 
square inch would be required to strip the screws or 
tear the stays themselves asunder." To test this mat- 
ter still further, Mr. Fairbairn had a new box made with 
£ inch copper on one side, and f inch iron on the other, 



STEAM-BOILER EXPLOSIONS. 27 

stayed with f inch screw stays, well fitted and riveted 
over, and placed five inches from centre to centre ; and 
this stood a pressure of seven hundred and eighty-five 
pounds to the square inch, with a bulging of the sides 
of less than ^ inch, and yielded by drawing the head 
of one of the stays through the copper, at eight hundred 
and fifteen pounds per square inch. Eegarding this, 
he says : " The above experiments are at once conclu- 
sive as to the superior strength of the flat surfaces of 
a locomotive fire-box, as compared with the top, or 
even the cylindrical part, of the boiler." 

The boiler of an engine exactly like the one that ex- 
ploded, by the same builders, of the same age, and 
that had run about the same number of miles, was 
tested ; and one of the " bolts of the cross-bar over the 
fire-box broke," at a pressure of 207| pounds per 
square inch ; but the appearance of the exploded boiler 
was such, that Mr. ^airbairn concluded that its crown 
sheet did not yield first, and that it " could not have 
burst under a pressure of less than three hundred 
to three hundred and fifty pounds upon the square 
inch." 

In all these cases of explosion caused by a steady 
increase of pressure, reported by Mr. Pairbairn, it is 
seen that his knowledge of the strength of materials 
leads him to the opinion that they were caused by very 
high pressures ; and it is undoubtedly true that quite a 
large proportion of the explosions, caused by a steady 
increase of pressure without overheating, take place 
at pressures very much above those at which the boilers 
are designed to work. 



28 STEAM-BOILER EXPLOSIONS. 

As bearing upon this part of the subject of the 
strength of boilers to withstand a steady pressure, it 
will not be out of place to mention the case of an old 
boiler which I tested several years ago. This was forty- 
two inches in diameter, about twenty-eight feet long, 
with two twelve-inch flues through it. The heads were 
of cast iron ; the iron in the shell appeared to have 
been originally T 5 g of an inch thick, and that in the 
flues T 3 g of an inch. It had been in use over twenty 
years, and it was known that the water had been so 
low in it, at one time, as to lead to the supposition 
that it might have been seriously injured by the over- 
heating ; it had also a heavy indentation on its lower 
side, caused by a settling of the front, thereby bringing 
too much weight upon a little pier on the bridge wall ; 
yet it stood a pressure of two hundred and forty 
pounds per square inch without a sign of yielding. 

Notwithstanding this great strength of good boilers, 
it is undoubtedly true that there have been explosions 
of boilers at their ordinary working pressures, without 
overheating, and without sudden increase of pressure, 
because of defects in material, design, or workmanship. 
As, for example, a plate that has to be flanged may be 
so poor, or worked with so little skill, as to have so 
little strength left in the bend, that a little alteration 
of form, from variation of pressure, on account of the 
defective staying of the flat part of the plate, may 
cause a break, that, above the water-level, may lead 
to explosion. 

A boiler may be so poorly stayed that a very little 
corrosion, around an imperfect weld in one of the stays, 



STEAM-BOILER EXPLOSIONS. 29 

may lead to explosion. Or a plate may have its 
strength so reduced, at and near a longitudinal seam, 
in punching, bending, pinning, and riveting, that the 
little alteration of form that takes place at this point 
at every variation of pressure, may cause a break, par- 
ticularly in a wide plate, that will lead to an explosion ; 
or a leak from such a source may, by corrosion, so re- 
duce the strength of the iron at that point, that, in 
combination with the alteration of form, an explosion 
may ensue. 

Explosions have been caused by blisters, where the 
imperfect weld in the plate has been so large, and so 
near the side next the water, as to leave so little 
strength, after the side of the plate next the fire has 
parted off, with the consequent loss of its strength be- 
cause of elevation of temperature, as to be ruptured 
by the ordinary working pressure. 

Explosions have occurred from overheating caused 
by the presence of scale and sediment. They may be 
caused by the overheating of the bottom of the boiler 
by the presence of scale, that adheres to the iron over 
a limited surface, till its power of resistance is reduced 
below that of the ordinary working pressure of the 
boiler, so that a rupture occurs, large enough, perhaps, 
to merely throw the boiler out of place, or, it may be, 
extends so as to cause a violent explosion ; or the ex- 
plosion may be caused by an overheating, not so high as 
to seriously reduce the tensile strength of the iron, but 
of so much of the surface of the bottom of the boiler, 
as, by the strain from unequal expansion, to cause a 
break through a " round about " seam ; or by a scale 



30 STEAM-BOILER EXPLOSIONS. 

which adheres till the boiler becomes so much over- 
heated where the heat is most intense, as that the 
expansion of the iron shall detach scale enough to 
cause the breaking of the bottom of the boiler, by the 
combined action of the strain caused by the contraction 
of the uncovered part of the boiler, and the local 
pressure of the steam suddenly generated under water ; 
or it may be caused by the detachment of a considerable 
surface of scale from the bottom of the boiler, when the 
temperature of the uncovered part is but very little 
above that of maximum vaporization, which may cause 
the breaking of its top by the blow from the water put in 
motion by the sudden generation of steam on the bottom. 

A boiler may be caused to explode by an overheating 
caused by the presence of loose, heavy scale, that, 
after accumulating on the surfaces of the boiler, be- 
comes detached, and accumulates over the fire. In 
several instances I have known this scale to become 
detached from boilers just after they had been cleaned 
out, when it was supposed that all was removed that 
it was possible to get off, and to be deposited in a heap 
exactly over the hottest part of the fire, leaving the 
other parts of the boiler as clean as if they had just 
been swept. This loose scale does not adhere to the 
boiler so as to become detached by its expansion, but 
follows down on the iron till the rupture occurs. 

Regarding scale and deposits of sediment, the Com- 
mittee of the Franklin Institute say : " The undue 
heating of parts of a boiler may be produced by de- 
posits. No cause of undue heating is better made out 
than this : the least that can happen after the accumu- 



STEAM-BOILER EXPLOSIONS. 31 

lation of sediment is the injury of the boiler, — 
perhaps its bursting, — and a true explosion may 
result. Two violent explosions — at Bowen's Mill, and 
at McMickle's Mill, in Pittsburg — are fairly attribu- 
table to the effect of sediment; and there does not 
appear, in either case, to have been a deficiency of 
water. M. Arago mentions an instance of a rent 
made in a boiler, at Paris, by the accidental resting 
of a rag on the bottom of the boiler." 

We now come to the consideration of those ex- 
plosions, of which there have been so many, occur- 
ring when it was known that the pressure was not 
above the ordinary working pressure, and that the 
water was not low ; when there was no appearance of 
overheating on any part of the boiler, when examined 
after the explosion, and when, from the most careful 
examination, there were no indications of weakness 
that could account for the explosion ; in fact, in many 
instances, the indications being that the boiler, a 
moment before the explosion, was very much stronger 
than many boilers running without a leak, or sign of 
failure, under the same pressure of steam ; and in 
some instances parts of the exploded boiler itself, that, 
to all appearance, were very much weaker than the 
ruptured parts, were not only not broken, but showed 
no sign of having been subjected to a severe press- 
ure, even where the top of the shell was completely 
shattered. 

In relation to these cases, Mr. Colburn says : " Yet 
those who have given any attention to the subject of 
boiler explosions are aware that they frequently occur 



32 STEAM-BOILER EXPLOSIONS. 

when, without any overheating of the plates, the 
pressure stood, but a moment before, at the ordinary 
working point. In the case of the locomotive boiler 
which exploded in the summer of 1858, at Messrs. 
Sharp, Stewart, and Co.'s, at Manchester, the pressure, 
as observed upon two spring-balances and a pressure- 
gauge, stood at 117 pounds to 118 pounds a minute 
before the explosion, both valves blowing off freely at 
the time. The part of the boiler which exploded was 
the ring of plates next the smoke-box, out of the 
influence of any part of the fire. The fact, therefore, 
of the violent explosion of a strongly made boiler at 
117 pounds is a proof that it is not necessary to 
assume and to account for the existence of any press- 
ure above that point. On the 5th of May, 1851, a 
locomotive engine, only just finished, burst its boiler 
in the workshop of Messrs. Rogers, Ketchum, and 
Grosvenor, at Paterson, U.S. I was on the spot but 
a few moments afterwards, and found the effects of the 
explosion to be of the most frightful character : a con- 
siderable portion of the three-story workshop being 
blown down, whilst four men were instantly killed, 
and a number of others were injured, one of whom 
died soon afterwards. Several of the men, who, 
although immediately about the engine at the time, 
escaped unhurt, unanimously declared that the safety- 
valves were blowing off before the explosion, and that 
the two spring-balances indicated, but a moment before 
the crash, a pressure of but 110 pounds per square 
inch." 

These are cases of the explosion of boilers at press- 



STEAM-BOILER EXPLOSIONS. 33 

ures that, without proof to the contrary, may be taken 
to be very much below their powers to resist pressure 
unaccompanied by shocks. In one instance of ex- 
plosion that I investigated in 1854, there was no 
appearance of overheating on any part of the boiler, 
or evidence that the pressure was over 80 pounds 
per square inch a moment before the explosion. The 
top of the shell was broken up so as to lead to the 
supposition that the iron must be very poor ; but on 
testing a strip cut from one of these small, brittle- 
looking pieces, that had been blown out clean, I found 
it to be stronger than new Low Moor, or Bowling iron, 
tested at the same time. The new Bowling iron broke 
at 55.632 pounds per square inch; the new Low 
Moor, at 56.704 pounds; and that from the exploded 
boiler, at 58.250 pounds. 

And in a case that I investigated in 1856, in which 
the top of the shell of a locomotive was pretty much 
all blown off when the engine was running on the road, 
under a pressure of about 100 pounds per square inch, 
two strips of iron cut from a piece of the exploded 
boiler broke, one with 43.392 pounds per square inch, 
and the other a very little under : these strips were 
cut from a little piece, blown out of the plate in the 
top of the shell, that appeared to have, been the first 
to yield; and its weakness would indicate that the 
boiler might have yielded to overpressure. But that 
overpressure was not the cause of the explosion, was 
proved by the fact that parts of the flat surfaces of the 
fire-box, which were so weak, because of broken screw 
stays, as that they must have yielded to a pressure 



34 STEAM-BOILER EXPLOSIONS. 

very much below that which would have caused the 
rupture in the shell, — even if the unbroken stays and 
the plates of the fire-box were of iron of the maximum 
strength, — were not opened in the least. The broken 
stays were in the upper row of the sides of the fire-box, 
and it was perfectly evident they had been broken 
for a long time ; but the sides of the fire-box and the 
crown sheet stood up square and good. In this case, 
it was noticed, in leaving the station just before the 
explosion, that the water was not working right. I 
was told, " She had so much water in her that she 
could hardly be got away from the station," and the 
fire-box ends of the copper tubes showed clearly that 
they had been overheated. But it was not clear how 
much of this overheating might have been done after 
the boiler exploded, particularly as it was known that 
there was a heavy fire at the time, which was not 
removed till some little time after the explosion. But 
from the fact that tubes which were very nearly closed 
up by the explosion, and through which there was no 
passage for the heat, had so nearly the same appear- 
ance as others that were not so closed, I am satisfied 
that a part at least of this overheating was done before 
the explosion ; and that the explosion was caused by 
overheating below the level of the water, and around 
the fire. The engineer was killed, and the fireman 
injured ; but the latter told me he saw the engineer 
try the water but an instant before the explosion, and 
it was high enough ; the trouble with the water at the 
station had so called his attention to the fact that it 
was not working right, that he was watching it con- 
tinually. 



STEAM-BOILER EXPLOSIONS. 35 

Mr. Colburn, in speaking of this class of explosions, 
says : " Locomotive boilers have burst in the plates 
next to the smoke-box, beyond the reach of the fire, 
and where the boiler is believed to be stronger than 
about the fire-box. As has been observed, the dome, 
if it open from the ring of plates in question, weakens 
it materially ; but explosions have occasionally occurred 
in this part of a boiler, either having no dome, or 
having one only over the fire-box. A fact which was 
some time since communicated to me by George S. 
Griggs, Esq., Locomotive Superintendent of the Boston 
and Providence Railroad, U.S., may assist in explain- 
ing this somewhat anomalous mode of explosion. In 
one or two cases of locomotive boiler explosions, Mr. 
Griggs found, upon examination, that whilst none of 
the upper tubes had been burnt, others, lower down, 
exhibited unmistakable indications of having been 
smartly scorched; the solder used in brazing being 
more or less melted." 

That the explosions now under consideration are 
caused by an overheating near the bottom of the 
boiler, causing the water to be thrown with such 
force as to break the top, I think there can be no 
doubt. Mr. Rankine (see his " Manual of the Steam 
Engine and other Prime Movers ; " London and 
Glasgow: Richard Griffin & Co., 1859) says of this 
class of explosions : " There is much difference of 
opinion as to some points of detail in the manner in 
which this phenomenon is produced ; but there can be 
no doubt that its primary causes are, first, the over- 
heating of a portion of the plates of the boiler (being 



36 STEAM-BOILER EXPLOSIONS. 

in most cases that portion called the crown of the fur- 
nace, which is directly over the fire), so that a store of 
heat is accumulated ; and, secondly, the sudden contact 
of such overheated plates with water, so that the heat 
stored up is suddenly expended in the production of a 
large quantity of steam at a high pressure. Some en- 
gineers hold, that no portion of the plates can thus 
become overheated, unless the level of the surface of 
the water sinks so low as to leave that portion of the 
plates above it, and uncovered ; others maintain, with 
M. Boutigny, that when a metallic surface is heated 
above a certain elevated temperature, water is pre- 
vented from actually touching it, either by a direct 
repulsion, or by a film or layer of very dense vapor ; 
and that when this has once taken place, the plate, 
being left dry, may go on accumulating heat and 
rising in temperature for an indefinite time, until 
some agitation, or the introduction of cold water, shall 
produce contact between the water and the plate, and 
bring about an explosion." 

Mr. Bourne, in the eighth edition of his " Treatise 
on the Steam Engine," London, 1868, in relation to 
this matter, says : " There can be no doubt that the 
water is sometimes repelled from the metal in the same 
manner as would be done if it were in the spheroidal 
state; and explosions have, no doubt, had their origin in 
this phenomenon. The water appears to be repelled 
from the iron in those parts where the heat is greatest." 

Mr. Colburn, in speaking of the rising of water 
because of the condensation of the steam above the 
water, says, regarding the force of the blow given by 



STEAM-BOILER EXPLOSIONS. 37 

it : " In this case ... it would not be necessary to 
assume the existence of any defect in the boiler ; for, 
when the water once struck violently, the soundest 
iron would probably be broken, and the strongest 
workmanship destroyed." 

The experiments of the Committee of the Franklin 
Institute demonstrated that the temperature of maxi- 
mum vaporization of a clean, rough, iron surface, — 
like that of a clean iron steam-boiler, — is 346|° F., 
and that the temperature of perfect repulsion for the 
same is 385° F. ; and the temperature of maximum 
vaporization for iron, " highly oxidated but clean," is 
381° F., and that of perfect repulsion for the same 
is 433° ; the temperature of maximum vaporization 
of polished copper is 292°, while that of perfect re- 
pulsion is 315° ; for the same oxidized, the temperature 
of maximum vaporization is 317°, while that of perfect 
repulsion is 338° ; for copper very much oxidized and 
not clean, the temperature of maximum vaporization 
is 348°. 

The Committee say, in relation to this matter : " The 
time of vaporization is less in the copper than in the iron, 
in the ratio, probably, of two to one, or nearly in the ratio 
of their conducting powers for heat, which are two and 
one half to one. ... A repulsion between the metal 
and the water is perfect at from twenty to forty degrees 
above the point of maximum vaporization, following 
more closely upon the temperature of maximum vapor- 
ization in copper than in iron. At these tempera- 
tures the water does not wet the metal. . . . There 
can be no doubt, that at the temperatures determined 



38 STEAM-BOILER EXPLOSIONS. 

as those of maximum vaporization, an effective force 
of repulsion between the heated metal and the water 
has begun to be developed. 

Regarding the effect of pressure upon the points of 
maximum vaporization, and of repulsion, the Commit- 
tee say : " It is possible, and indeed probable, that 
pressure may modify these results, all of which were 
obtained u'nder atmospheric pressure. Pressure, tend- 
ing to counteract the effect of the repulsion between the 
heated metal and the water, would probably raise the 
temperature of most rapid vaporization." 

With regard to the effect of pressure in a steam- 
boiler upon the point of perfect repulsion, my experi- 
ments have demonstrated that pressure, accompanied 
by a rapid circulation of the water, does so far over- 
come the repulsive action of the heat, that practi- 
cally the point of repulsion may be said to be raised 
by the pressure within the boiler ; but that this only 
holds true so long as there is perfect circulation of the 
water ; and that in a steam-boiler, when the circulation 
of the water is not perfect, pressure does not appear to 
have any effect whatever upon the temperature of re- 
pulsion. So that a steam-boiler working under one 
hundred pounds pressure, the surfaces of which are 
of such a character that the temperature of perfect 
repulsion at atmospheric pressure is 385°, will be liable 
to just as perfect repulsion from any of its surfaces 
exposed to an intense heat, whenever that temperature 
is reached, unless the circulation of the water within 
the boiler is so good that it shall be continually 
brought into forcible contact with such surface ; and 



STEAM-BOILER EXPLOSIONS. 89 

that the combined action of pressure and of this per- 
fect circulation of the water is such, that water may 
be kept in contact with surfaces exposed to an intense 
heat, even up to pressures so high that the temperature 
of the water in the boiler is above that of perfect re- 
pulsion for the surfaces; in this case, however, my 
experiments show that the temperature of maximum 
vaporization is not changed ; or if changed at all, 
not so changed but what it is passed, so that the power 
of the repulsive action is so effective as that, notwith- 
standing the combined action of the circulation and of 
the pressure, the vaporization is decreased. 

In my experiments, — which were made to enable 
me to perfect my Safety Plugs, and to get exact pro- 
portions of the metals used for securing their conduct- 
ing rods to the cases, — it was necessary that the 
conditions should be as^ nearly the same as in the case 
of boilers in use, as possible ; and to this end, the plugs 
designed for the lower parts of the boilers were tested 
by putting them in the bottom of the experimental 
boiler, and causing the blast to act upon them, and 
upon the parts of the boiler around them. It was 
found, soon after the commencement of the experi- 
ments, that the variation in the results, because of the 
imperfect circulation of the water in the boiler, were 
so great, — notwithstanding the making of alterations 
which promised to remedy the defect, and the taking 
of the utmost care to keep the boiler free from any 
thing having a tendency to cause imperfect circulation, 
and also the reduction of the intensity of the heat on 
the conducting-rods, from which, because of the nature 



40 STEAM-BOILER EXPLOSIONS. 

of their surfaces, repulsion would take place at a lower 
temperature than from the boiler, — that they were 
of no value as showing the exact pressure required to 
blow out the conducting-rods. I then had a boiler 
made, in which the circulation of the water was so 
strong, around and against the plugs, that, when the 
boiler was clean, it would stand a power of blast strong 
enough to raise the pressure from sixty pounds to three 
.hundred and sixty pounds per square inch, in from eight 
and one half to nine minutes, without such a repulsion 
from the conducting-rods as to overcome the combined 
power of the pressure and of the circulation, so as 
to seriously affect the results. I was then enabled to 
complete the work of perfecting the plugs and of get- 
ting the exact proportions of the metals for them ; and 
in doing this, and by experiments then made with the 
first-mentioned boiler, the facts indicated above, in 
relation to the effect of pressure upon the points of 
maximum vaporization, and of perfect repulsion, were 
brought out ; also the fact that a variation in the qual- 
ity of the water, so slight as not to be apparent to the 
taste, or to affect its color, as seen in a glass vessel, 
did affect its circulation in a steam-boiler, in its rela- 
tion to the point of perfect repulsion ; and also, that 
whenever any part of the surface of a steam-boiler, 
much below the surface of the water, is raised much 
above the temperature of maximum vaporization, the 
reduction of its temperature to that point is attended 
with such a vaporization of water as to endanger the 
boiler. Taking the temperature of maximum vapori- 
zation of the copper conducting-rods, in the condition 



STEAM-BOILER EXPLOSIONS. 41 

in which they were in the boiler daring the experi- 
ments, to have been 320°, and their temperature of 
perfect repulsion to have been 340°, it will be seen that 
at a pressure of one hundred and forty pounds to the 
square inch, the temperature of the water within the 
boiler, and having the temperature due its pressure, is 
above that of repulsion, and that the conducting-rod 
and its surrounding case must, when the full power of 
the blast was on them, have been at a higher tempera- 
ture than the water. The conducting-rods and cases 
are of pure copper, and their construction and arrange- 
ment are such as are calculated to reduce this differ- 
ence in temperature to the minimum ; but still, their 
temperature must, with the blast on, be above that of 
the water within the boiler, even before the point of 
maximum vaporization is passed. So that the fact 
that a conducting rod — brazed in with a metal that 
is known will have its strength so reduced by an ele- 
vation of temperature above 340°, that it will be broken 
by the pressure due that temperature, and the rod 
blown out — is not blown out below that pressure, 
when acted upon by a powerful blast, is proof that the 
power of the repulsive action of the heated rod and its 
case upon the water has not been sufficient to keep the 
water from the rod, so that its temperature has been 
elevated much above that of the water within the 
boiler. 

This fact was demonstrated by the repeated testing 
of plugs above the temperature of perfect repulsion at 
atmospheric pressure, and as high as a pressure of 
three hundred and sixty pounds per square inch above 

4 



42 STEAM-BOILER EXPLOSIONS. 

the atmosphere, and consequently to a temperature 
nearly 100° abpve that of repulsion. 

That the power overcoming the repulsive force in 
these cases was not that of pressure alone, was demon- 
strated in this way : after the perfecting of the plugs, 
and getting the exact strength of the metals, so that it 
was known at what pressure a conducting-rod would 
be broken from its case when the temperature was 
that due the pressure, they were tested in the first 
mentioned boiler, in order to learn how much their 
strength would be reduced by any elevation of tem- 
perature because of a repulsion of the water from the 
parts acted upon by the blast ; and it was found that 
the repulsion in some instances was such that con- 
ducting-rods, so strong as to stand a pressure of three 
hundred and sixty pounds per square inch, with a 
power of blast that raised the pressure from sixty 
pounds to three hundred and sixty pounds, in from 
eight and one-half to nine minutes, would be blown 
out at pressures below ten pounds per square inch. 

That pressure on the boiler did not have the least 
effect upon the power of repulsion, was shown by the 
fact that when the pressure was raised to fifty pounds 
per square inch, — at which pressure the temperature 
of the water within the boiler would be more than 
40° below that of perfect repulsion, — by a power of 
blast so moderate that there was no appearance of a 
repulsive action, when the full power of the blast was 
turned on, the perfect repulsion took place just as 
quickly as when the pressure was but one pound per 
square inch, when the full blast was turned on. 



STEAM BOILER EXPLOSIONS. 43 

In making these experiments, the heat was confined 
to the lower part of the boiler ; so that when the re- 
pulsion was perfect, the water was so elevated into the 
upper part of it, out of the reach of the direct action 
of the blast, that the loss by radiation caused a re- 
duction of the pressure. And in some instances the 
repulsive action was so strong, that the water was kept 
so still in the upper part of the boiler, as long as the 
blast was maintained, that the steam-gauge showed a 
steady decrease of pressure, with hardly a sign of 
agitation within the boiler. The return of the water 
to the bottom of the boiler, after the shutting off of the 
blast, was always attended with violent fluctuations of 
pressure, very much more violent than were ever pro- 
duced while the repulsive action was being developed. 

That the surfaces of a steam-boiler which are ex- 
posed to the most intense heat may be maintained at 
a temperature above that of maximum vaporization, 
and below that of perfect repulsion, the power of 
repulsion, and that of the combined action of the 
circulation of the water and of the pressure, so nearly 
balancing each other, that, so long as there is no fail- 
ure in the circulation, the temperature of such sur- 
faces will be kept below the temperature of perfect 
repulsion ; and that, when this is the case, a reduction 
of the intensity of the fire is attended with a violent 
vaporization of water, — was demonstrated in this way. 
As before mentioned, I tested a great number of plugs 
with a strong blast, and at pressures so high that the 
temperature of the water within the boiler, having 
the temperature due the pressure, was much above the 



44 STEAM-BOILER EXPLOSIONS. 

temperature of perfect repulsion for their surfaces 
under atmospheric pressure, without the development 
of such a repulsive action as to lead to an elevation of 
temperature so great as to seriously reduce the strength 
of the brazing of the conducting-rods ; showing clearly 
that the combined action of the pressure and of the 
circulation did so far overcome the power of repulsion 
as to practically elevate the point of perfect repulsion. 
At the commencement of these experiments, it was the 
practice to turn off the blast at a pressure approaching 
that at which it was supposed the conducting-rod would 
be blown out, in order to observe its appearance ; but 
it was found that in many instances, in a time varying 
from one to four or five seconds after the blast was 
turned off, the rod would be blown out. This occurred 
at pressures all the way up to over three hundred 
pounds per square inch above the atmosphere. Rods 
were blown out in this unaccountable way, as it then 
appeared to me ; and at pressures so much below the 
supposed strength of the metals, as to defeat the object 
sought, which was the getting the exact strength of the 
metals at known temperatures. This practice of turning 
off the blast was kept up for some time after it was clear 
that the results were of very little value as showing 
the exact strength of the metals, because of a desire 
to subject each of quite a large lot of metals, varying 
very much in strength, to exactly the same treatment. 
The practice was then changed: the blast was not 
turned off after approaching the breaking point of the 
metals, and the experiments were repeated with much 
care ; and then, after getting the exact strength of the 



STEAM-BOILER EXPLOSIONS. 45 

metals, it was perfectly evident that the turning off of 
the blast was followed by an explosive vaporization 
of water by the conducting-rod ; showing that the 
temperature of the conducting-rod, when the blast was 
on, was above that of maximum vaporization ; and 
that the violence of the result was due to the reduction 
of temperature to that point, and to the then explosive 
vaporization of a little water before the inertia of that 
above it could be overcome. 

The water used in these experimental boilers was 
all drawn from the same pipe, and great care was 
taken to keep the boilers clean ; and yet there was a 
very noticeable difference in its working in the boilers, 
in relation to the matter of repulsion, from day to day, 
which manifested itself in the difference in power of 
blast required to produce perfect repulsion, the length 
of time after the blast was turned off before the return 
of the water to the overheated surfaces, and in the 
difference in the elevation of temperature above that 
of maximum vaporization, when the point of perfect 
repulsion was not reached ; when all the other condi- 
tions appeared to be the same. 

It thus appears that during these experiments there 
were many genuine explosions, the effects of which, 
owing to the great strength of the boilers and the 
comparative weakness of the safety plugs, were con- 
fined to the plugs, they having broken by the first 
explosive burst of steam, so that the water was not 
thrown with sufficient force to break the boiler ; or 
in the case of a continued perfect repulsion, yielding 
to the pressure at a temperature far below that at 



46 STEAM-BOTLER EXPLOSIONS. 

which the strength of the boiler was seriously re- 
duced ; and that, while in the explosions of this 
class (a continued perfect repulsion) there were such 
indications of trouble within the boiler, that an en- 
gineer, who was familiar with the working of the 
boiler, and who was watching the steam-gauge and the 
water at the time, would have his attention called to 
the fact, — there were in the other class (that in which 
perfect repulsion was not established) no indications 
whatever of trouble in the boiler till the plugs broke ; 
so that it would be impossible for an engineer, by any 
examination he could make, to know that there was 
the least trouble with the boiler up to the instant of 
the explosion. 

It is this class of explosions, and those to be consid- 
ered farther on, caused by the overheating of the water, 
that have led to so many theories of explosive gases 
and mixtures. It is known to all who have had expe- 
rience in the examination of exploded boilers, and also 
in the testing and inspecting of old boilers that have 
not exploded, that there are many boilers in use that 
are defective in construction, with poor safety-valves 
on them, gauge-cocks half choked up, and with large 
accumulations of sediment or scale in them, so that it 
is hard to understand why they have not exploded ; 
while, in many instances of explosion, there are no 
such indications of weakness, or of defective fittings 
or condition. I never saw but one exploded boiler 
that bore evidence of having been in so bad condition 
as very many that I have tested and inspected that 
were not even suspected, before the examination, of 



STEAM-BOILER EXPLOSIONS. 47 

being in a dangerous condition. In many instances 
of these explosions of strong clean boilers, experts 
have either had to acknowledge that they did not 
know the cause, or to report that the water must 
have been low ; that the safety-valve must have been 
fastened down ; or that, notwithstanding the apparent 
strength of the boiler, there must have been some 
hidden defect in its construction or material. 

Now, in order to the better understanding of the 
causes that produce an explosion of the class under 
consideration, let us take the case of a boiler in which 
the surfaces around the fire are clean and smooth, and 
very nearly uniform, and in which the circulation of the 
water is ordinarily good, but which has now got some 
element in the water that favors repulsion, or causes 
the water to circulate sluggishly, working with so 
strong a fire that the surfaces exposed to the most in- 
tense heat shall be raised to a temperature very near 
that of maximum vaporization, but not above it, so 
long as the steam pressure is maintained. Now, let 
the demand for steam be increased, so that there shall 
be such a sudden reduction of pressure that the de- 
scending current shall give off steam, and the circu- 
lation will be so broken up that the temperature of 
the surfaces around the fire will be raised above that 
of maximum vaporization : this will cause a decrease 
in the steaming power of the boiler, so that, without a 
greater demand for steam, the reduction of pressure 
will be more rapid, with its consequent interference with 
the circulation of the water, and thus the temperature 
of these surfaces be rapidly raised to that of perfect 



48 STEAM-BOILER EXPLOSIONS. 

repulsion. Now, let the demand for steam be so far re- 
duced that the boiler shall make steam as fast or a lit- 
tle faster than it is used, and let a fire-door be opened 
and a strong current of cold air be thrown upon the 
overheated surfaces, their temperatures will be so 
reduced that the water will return upon them and 
complete the reduction to the temperature of maxi- 
mum vaporization, with the consequent violent vapor- 
ization of such an amount, that the steam so gen- 
erated shall throw the water above it with such force 
as to break the shell of the boiler, and so cause its 
explosion. 

Or, without the opening of the door, let the demand 
for steam be so reduced as to lead to a rapid rise in 
pressure, and the interference with the descending cur- 
rent ceases ; the circulation of the water is soon so 
strong as to overcome the repulsive power ; the over- 
heated parts are reduced to the temperature of maxi- 
mum vaporization, and the water is thrown by the 
steam generated under it with such force as to break 
the shell of the boiler, and so cause its explosion ; — 
without, in either case, any part of the boiler having 
been overheated so as to show it after the explosion, or 
so as to have reduced its tensile strength in the least. 

I am of the opinion that a large proportion of the ex- 
plosions of locomotives occurring while on the road, or 
just after arriving at a station, are caused by their shells 
being broken by water thrown from overheated plates 
considerably below the surface of the water, and that 
this is true of most boilers that have the upper part of 
their shells blown off, without the throwing of the 



.STEAM-BOILER EXPLOSIONS. 49 

lower part of the boiler. Mr. Colburn gives six cases of 
violent locomotive explosions, in which the engines did 
not leave the rails, — in two of which the fact is men- 
tioned that they occurred just after the shutting off of 
the steam, — and says: "Comparatively few locomo- 
tive boilers ever leave the rails when they explode, un- 
less the roof of the inside fire-box is crushed down." 
The locomotive mentioned on pages 33, 34, did not 
leave the rails ; and the boiler mentioned on page 33 
was hardly moved from its place, the tops in each of 
these instances being completely shattered. When 
explosions are caused by overpressure, boilers are 
usually thrown to a greater or less distance ; as is 
shown clearly by the cases given by Mr. Fairbairn, on 
pages 22, 23, 24, 25, and 26. 

Now, as to the force with which the water is thrown 
from an overheated surface. Prom the force of the 
bursts during my experiments, I am of the opinion 
that the return of water upon clean iron surfaces much 
below the surface of the water, after a repulsion, espe- 
cially when the return is aided by a reduction of tem- 
perature on the fire side, will result in an instant rise 
to a very great pressure before the inertia of the water 
is overcome. I think that with four feet of water 
over the place, this momentary pressure might be even 
three hundred pounds per square inch or more, above 
that — beyond the reach of this local action — on the 
boiler at the time ; and that, in all cases where there is 
much surface overheated 'at any great depth below the 
surface of the water, and where, either from a sudden 
reduction of temperature on the fire side, or from the 



50 



STEAM-BOILER EXPLOSIONS. 



rapid rise of pressure from the reduction of demand 
for steam, there is a strong return of the water to the 
overheated surfaces, the water is thrown with such 
force as to hreak the shell of the strongest boiler 
in use. 

In the cases, like some of those given by Mr. Col- 
burn, where the shells of locomotives were broken just 
back of the smoke-boxes, the water is evidently thrown 
from the tube-plate and from the sides of the fire- 
box at the same time, giving a forward and upward 
direction to the water. In the cases given on pages 
33 and 34, the water was thrown against the shell, 
over, or just back of, the fire-boxes. In my experi- 
ments, the conducting-rod yielded to the pressure that 
would have thrown the water ; and boilers sometimes 
yield in the same way, the overheated surfaces not be- 
ing strong enough to hold till the inertia of the water 
is overcome. In one instance of this kind that came 
to my knowledge, the lower part of the fire-box tube- 
plate of a locomotive yielded to the pressure by strip- 
ping the threads and riveting of ten or twelve screw 
stays ; but the steam which had caused the burst then 
escaped into the fire-box, so that the local pressure 
was removed ; and although the strength of the parts 
was so reduced by the stripping of so many stays, they 
withstood the pressure of one hundred and twenty 
pounds on the boiler at the time. This engine, which 
was a first-class passenger engine, but two or three 
years old, had just stopped at a station, and the fire- 
man had had the fire-door open with the blower 
on, and was just in the act of closing it, or had just 



STEAM-BOILER EXPLOSIONS. 51 

closed it, when the burst occurred, and he was killed 
by the rush of steam from the fire-box : there had been 
no such marked defect in the circulation of the water 
in this boiler as to attract attention, nor was the over- 
heating sufficient to show the fact after the rupture. 
The stripped stays were |- of an inch in diameter, and 
there was no appearance of any imperfection in them, or 
in the plate forced off, or in the workmanship ; but the 
stays were placed 5J inches from centre to centre, and 
to this fact is due the stripping of the stays, and the 
saving of the boiler ; for there can be no doubt what- 
ever, that if these stays had been a very little nearer 
together, the water would have been thrown, and a 
first-class explosion would have been the result. 

Taking the results of the experiments of Mr. Fair- 
bairn on the strength of such flat surfaces, stayed with 
well-riveted screw stays, as a guide, I am of the opin- 
ion that this tube-plate would not have been forced off 
in the way it was, at a pressure less than three or four 
times that on the boiler outside of this local action, at 
the time ; and the fact that the yielding did not extend 
to the destruction of the boiler, after the great reduc- 
tion of strength caused by the stripping of so many 
stays, and which would not be attended by a sensible 
reduction of pressure outside of the local action, while 
the plate was in motion, is a perfect demonstration 
that the plate yielded to a pressure very much greater 
than that on the boiler outside of the influence of this 
action, and that it was a local pressure that was in- 
stantly and entirely removed by the opening of the 
stay-holes. 



52 STEAM-BOILER EXPLOSIONS. 

I am confident that explosions of this class have 
had their origin in overheating, resulting from the 
surfaces around the fire having become coated with 
some substance or~substances that favor the repulsive 
action, so as to lead to the overheating by a compara- 
tively moderate fire ; the coating remaining unchanged 
till there is a certain elevation of temperature (above 
that of maximum vaporization), and then being en- 
tirely removed, or its character so changed by the 
elevation of temperature, as to leave a surface of such 
a character that its temperature will be reduced so 
fast from the circulation of water within the boiler, 
without any great increase of pressure, or without any 
reduction of temperature on the fire side, as to lead to 
the throwing of the water and destruction of the 
boiler. 

I think this is the case in most new boilers, like 
those of the new locomotives given by Mr. Colburn on 
page 32 ; * and it is probable that in many of the 
explosions of this class the overheating is assisted, 
more or less, by some coating of this nature. In a 
case of the explosion of a cylindrical boiler, with the 
fire under its shell, the first time it was used, after the 
putting in of a new plate over the furnace, it was 
noticed, not long after steam was got up, that the 
new plate was so overheated as to cause the leaking of 

* In the case of the explosion at Paterson, mentioned by Mr. Col- 
burn, the crown-sheet of the boiler was weaker than the shell, so that 
when the water thrown up from the sides of the fire-box met above it, 
the shock caused it to yield, so that it was forced down and the engine 
thrown into the air. 



STEAM-BOILER EXPLOSIONS. 53 

its seams. The opening of the doors to reduce its 
temperature was followed in a few minutes by the 
explosion of the boiler. The overheating of this plate 
was undoubtedly due to a coating on it that favored 
repulsion ; and it is possible that the return of the 
water to it, after the change in its character, or its 
removal by the elevation of temperature, might have 
been so gradual as to have avoided the explosion, but 
for the sudden reduction of temperature on the fire 
side, caused by the opening of the fire-doors. 

The circulation of water in boilers is frequently 
affected by changes in the character of the water in 
them, apparently very slight, and which have in many 
instances been produced by some substance which has 
accumulated in the water-pipes, and been washed 
through into the boilers, without its presence being 
suspected ; and some water, that ordinarily circulates 
well, will be seriously affected by a very slight interfer- 
ence with the descending currents. Two boilers, about 
twenty-eight feet long, four feet in diameter, with two 
sixteen-inch flues in each, were set side by side, with 
one furnace under the two : they were exposed to the 
action of the flame and heated gases, to a point a-bove 
that of the middle gauge-cock, and in some places 
nearly up to the upper cock, but the brick-work was 
but little off from the boilers from the centre up on 
the outsides, and they were set so near together as to 
make the passage between them quite narrow, so that 
their surfaces were not exposed to a very intense heat, 
much above their centres. They were fed together, the 
feed-pipe connecting the two boilers without means for 



54 STEAM-BOILER EXPLOSIONS. 

separating them. The steam connection on top of the 
boilers was the same ; i.e., there was no valve between 
the boilers. They were used in this condition for 
more than seven years without any irregularity in 
the working of the water that attracted attention ; 
and then, without any change whatever in any of the 
arrangements, or in the water, other than what was 
caused by the introduction of something that had 
accumulated in the water-pipes, the water began to 
work in a very remarkable manner. When I exam- 
ined the boilers, the putting on of the feed-pump, 
when the water in them was at or a little below the 
middle gauge-cock, would be followed in a little time 
by a rush of water from one boiler into the other, so as 
to be solid water at the upper gauge-cock in the latter 
boiler, and dry steam at the middle cock in the boiler 
from which it went ; and then by a return, so that it 
would be solid water at the upper cock of the first 
boiler, and dry' steam at the middle cock of the other ; 
it would then settle down level in the two boilers, and 
show no sign of fluctuation by the variation of the 
intensity of the fires on the opposite sides of the fur- 
nace, such as shows itself when the steam connections 
of such boilers set together are too small. 

The first time I saw this operation of the water, it 
went, soon after the starting of the pump, first from 
the left-hand boiler into the right, then back into the 
left, and then settled down quietly. The second time, 
a few hours after, the starting of the pump was fol- 
lowed by a rush of water from the right-hand boiler to 
the left, and then back to the right, and then finding 



STEAM-BOILER EXPLOSIONS. 55 

its level, showing that the action was not caused by 
any peculiarity in the feed-pipe, which diverted the 
water into one boiler. This was also shown by the 
fact that the starting of the pump was not followed 
by any such action, when the water was much above 
the middle gauge-cocks at the time of starting it. 

The boilers were tested, and found to be strong and 
tight ; and examined, and found to be not very dirty, 
— that is to say, not having so much sediment in them 
as many boilers have without any trouble, — and no 
hard scale. The brick-work was found to be as indi- 
cated above, and was put down so as to confine the 
heat to the parts of the boilers below the lower gauge- 
cocks ; the boilers were cleaned out, but no changes 
made in the pipes ; and there was no more trouble 
with the water. 

I am of the opinion that this phenomenon was pro- 
duced in this way. The new element in the feed-water 
caused the coating of the boilers, in a way calculated 
to favor repulsion, but not to the extent of leading to 
repulsion so long as the water was up. Then as 
the water went down in the boilers, the one that had 
the strongest fire under it would have its upper 
surfaces uncovered faster than the other one, on ac- 
count of the more rapid vaporization of its water, and 
because this would keep the pressure in it above that 
in the other boiler, thus depressing the water.* This 
uncovered surface would also be exposed to a greater 

* The steam connecting-pipes were so large that this difference in 
pressure and water-level was very slight, except when the water was 
thrown over the overheated surfaces. 



56 STEAM-BOILER EXPLOSIONS. 

heat, so that the elevation of temperature would be 
so much greater than that of the uncovered surface in 
the other boiler, that the character of the coating near 
the front end of the boiler would be so changed by the 
elevation of temperature, that, when the water came 
up over it- soon after the starting of the pump, it 
would lead to such a reduction of the iron to its tem- 
perature of maximum vaporization,* as to cause the 
throwing of the water over the overheated surface, 
and among the superheated steam, which would lead 
to a sudden elevation of temperature, and to the 
oscillation of the water to the back end of the boiler, 
so that in a very short time all the overheated surfaces 
in this boiler would be reduced : this rise of pressure 
stopped the entrance of the feed-water into this boiler, 
and caused the water to rush through the feed-pipe 
with the water going into the other boiler. The 
boilers were fed with water at a low temperature, 
and near the bottom ; and the turning of it all into 
the other boiler would still further check its production 
of steam, and at the same time reduce the temperature 
of the gases around its uncovered surfaces ; so that 
when the water came up over them, the character of 
the coating (in relation to repulsion) on the parts 
of them last uncovered had not been so changed as 
to lead to so sudden a reduction of temperature as to 
cause the throwing of the water, till the surface high- 

* This action, taking place just at the surface of the water, would 
not be attended with any great local pressure, but would be sufficient 
to completely disperse the water over the overheated surface, and to 
cause its oscillation. 



STEAM-BOILER EXPLOSIONS. 57 

est up and that had been longest uncovered was 
reached, where the elevation of temperature had been 
sufficient to cause such a change in the character of 
the coating, as to lead to a repetition of the operation 
which had taken place in the other boiler, with the 
same results, except that the water came up over the 
uncovered surfaces of the other boiler before there 
was sufficient elevation of temperature to cause a 
repetition of the operation, and the water settled 
down to its level. 

In another case, that of a boiler in which the circu- 
lation of the water was ordinarily good, the accidental 
introduction of a very little foreign matter, from the 
washing of some oily aprons, caused the water to work 
in a very peculiar manner. The repulsion and agitation 
appeared to be confined to the lower surfaces, there 
being no undue foaming at the surface ; so that the 
appearance of the boiler, when I saw it at work, was 
such that I supposed the fact of so much water being 
thrown out mechanically mixed with the steam was 
due to the working of the water too high ; but working 
with less water did not mend the matter, and a more 
careful investigation led to the discovery of the cause 
of the trouble. 

In another instance, two sets of boilers had worked 
side by side for over twelve years, the feed-water being 
taken to them through the same pipe. The character 
of the water was such that there was ordinarily no 
trouble with the circulation when they were cleaned out 
twice a year. One set of these boilers was found to 
be leaking just after the other set had been cleaned out, 

5 



58 STEAM-BOILER EXPLOSIONS. 

and found to have very much less sediment in them 
than usual ; in fact, they had so little in them that the 
other set were not cleaned out, as they otherwise would 
have been. After the boilers began to leak I tested 
them, and found they had been so overheated that 
nearly every seam on the bottoms leaked. They were 
then examined inside, and the amount of sediment 
found to be larger and of a different character than 
was ever found in them before; showing clearly, as 
there had been no change whatever in the pipes, that 
a deposit of sediment somewhere in the water-pipes 
had been started when this set was being fed, and had 
all gone through into it. It did not lead to so marked 
a change in the working of the water on the surface as 
to attract attention, and its presence was unsuspected. 
Two plain cylinder boilers, sixteen feet long, and three 
feet in diameter, set side by side, with one furnace under 
them in which was a very strong fire, were found to 
work very badly when first started up : these boilers 
were supported by a cast-iron front, between which 
and the fire was a lining of fire-bricks. The back 
ends were supported by a wall about twelve inches 
thick, and the sides were exposed to the direct action 
of the flame to a point about four inches above the 
centre, a little below the lower gauge-cocks. The feed- 
water was introduced near the back ends, and was 
always at the temperature due the pressure on the 
boilers. After a few days' running, during which the 
water continued to work badly, the boilers were stopped 
and thoroughly cleaned out ; and I then fired them 
as hard as they could be driven without a sign of un- 



STEAM-BOILER EXPLOSIONS. 59 

steadiness in the circulation of the water for some 
hours after the steam was got up ; but then, as the 
brick-work got heated up, the circulation became more 
and more unsteady ; and, in about fourteen hours after 
the starting of the fires, the brick-work had become 
so heated, that the heat imparted by it to the boiler 
caused such an interference with the descending cur- 
rents, that the water would be thrown off by a fire 
of not over half the intensity that could be worked, 
without a sign of starting, when the brick-work was 
cool. The thickness of the back supporting-wall 
was increased, so as to offer more protection to the 
descending current there, and the brick-work on 
the sides brought down, so as to keep the heat from 
the descending currents there, till they could acquire 
sufficient momentum to carry them well down ; the 
making of these improvements in the brick-work 
protected the descending currents, so that the water 
worked very well. 

Two tubular fire-box boilers, in which the pro- 
vision for the circulation of the water was very good, 
that were worked with strong fires, had the circulation 
of the water so injured by the interference with their 
descending currents, caused by the partial filling up 
of their back water-legs by a loose scale from their 
tubes and waists, that a very large amount of water 
was thrown out mechanically mixed with the steam, 
but the water went through the engine without noise : * 



* It was a Corliss engine, and the large exhaust-ports on the bottom 
of the cylinder doubtless favored this. 



60 STEAM-BOILER EXPLOSIONS. 

the increase in the consumption of fuel was not noticed, 
because of changes in the machinery driven ; and there 
were no such indications on the surface of the water, 
of the trouble within the boiler, as to attract attention, 
so that their dangerous condition was not suspected. 

While the boilers were in this condition, it became 
necessary to learn the power required by the machines 
in the several departments ; and indicator-cards, taken 
for this purpose, showed that, when the machinery was 
all on, so as to require the engine to take steam very 
nearly half-stroke, if from any cause the pressure 
on the boilers was being reduced, the amount of water 
thrown over mechanically mixed with the steam was 
so large, that steam given off by it, because of 
the reduction of pressure within the cylinder after the 
closing of the steam-valve, was sufficient to raise 
the pressure at the end of the stroke nearly sixteen 
per cent. That this great overpressure at the end 
of the stroke was not an appearance only, caused by a 
defect in the indicator, or that it was caused by a leak 
in the steam-valves greater than that of the piston and 
exhaust-valves combined, is shown by these facts : 
that the indicator used was a very good instrument, 
and perfectly free at the time ; that the curves on the 
cards are not such as would be made by a leak of the 
steam-valves, — i.e., they run down regularly till the 
pressure is reduced so as to cause the water in the 
steam to begin to give off steam, and show the irregular 
line, while this was being done, to near the end of the 
stroke, where they again become regular ; and that a 
reduction of the load, letting the engine cut off quicker, 



STEAM-BOILER EXPLOSIONS. 61 

— so that the interference with the descending currents, 
caused by the reduction of pressure when the engine 
took steam, was less, — was followed by a reduction of 
the overpressure at the end of the stroke: the throw- 
ing off of about twenty per cent of the load reduced the 
overpressure at the end of the stroke to a little less 
than seven per cent. And the engine, which was only 
fourteen-inch cylinder, four-foot stroke, making fifty- 
two revolutions per minute, with ninety-seven pounds 
pressure on the boilers, was driving, when the machinery 
was all on, over one hundred and thirty indicated horse- 
power, and an average of nearly one hundred and twenty 
indicated horse-power through the day, with the con- 
sumption of but little over three pounds of ordinary 
anthracite coal per indicated horse-power per hour; 
and this with a safety-valve on the exhaust-pipe 
weighted so as to cause a pressure of over one and 
one-half pounds per square inch (the pressure re- 
quired to do the warming and drying) in the exhaust- 
pipe. 

We now come to the consideration of the class of 
explosions in which there is the same shattering of the 
upper part of the shell as in the class last considered : 
where there is no evidence of overheating, the explosion 
occurring after the boilers have been quiet for a greater 
or less time, with very moderate fires in them ; and, in 
some instances, when it is known that the pressure, but 
a moment before the explosion, was very low, — i.e., with 
the fires so moderate as to preclude the idea of repulsion, 
and with too low pressure of steam and consequent tem- 
perature of water (unless the water was at a tempera- 



62 STEAM-BOILER EXPLOSIONS. 

ture above that due the pressure) to shatter the boiler, 
even if there was a large break in the top. In one 
instance of this kind, — of a locomotive less than one 
year old, — the pressure, as shown by the steam-gauge, 
was noticed by the watchman but a moment before the 
explosion to be but forty pounds. In this case, the 
engine had been run into the house with the water 
well up, the night before, and had so stood through 
the night till the time for starting the fire for the 
morning train. The fire had been started, and 
the engine was standing with this moderate fire 
and low pressure of steam, when the explosion oc- 
curred. The fireman, who was standing by its side, 
was killed. The watchman, who had just been in 
conversation with the fireman, and had then observed 
the pressure, had started away, and escaped injury. 

This was an explosion of terrific violence : the top 
of the shell was torn completely open in all directions 
from a point nearly over the fire-box. The most care- 
ful examination did not show any defect in construc- 
tion or material, that would account for the yielding of 
the upper part of the shell at a pressure less than one 
vastly above that on the boiler a moment before the 
explosion. 

In another instance a boiler had stood with the fires 
banked up over night. The fireman, who was killed 
by the explosion, had orders to get up steam early in 
the morning : the time of his going to the fire-room 
was known ; and in a time after this so short as to pre- 
clude the possibility of any great rise of pressure, the 
boiler exploded with great violence. 



STEAM-BOILER EXPLOSIONS. 63 

Mr. Colburn reports one case of this class : " On the 
12th of February, 1856, the locomotive ' Wauregan' ex- 
ploded, after standing for upwards of two hours in the 
engine house of the Hartford, Providence, and Fishkill 
Railroad, at Providence, U.S. Only sufficient steam 
had been maintained in the boiler to enable the engine 
to be run out of the house ; but at the time of the explo- 
sion the engine had not been started, the engine-man, 
who was killed, being upon the floor, at the side of the 
engine, at the time. The boiler gave out in the ring of 
plates next behind the smoke-box." Mr. Colburn in 
this connection adds, that " destructive explosions often 
occur at pressures of ten pounds to twelve pounds per 
square inch in low-pressure boilers." 

In relation to this class of explosions, it is clear that 
a boiler may be so weak as to yield to a very low press- 
ure, or that a strong boiler may be broken when the 
pressure is very low, by water thrown after repulsion ; 
but it is also clear that the steam given off by water, 
on a reduction of pressure above it, cannot have a 
pressure above that due the temperature of the water ; 
so that in case of the rupture, from any cause, of the 
shell of a boiler in which the pressure is low, and 
in which the water has the temperature due its press- 
ure, it does not appear possible that the water and 
steam will be thrown with such force as to shatter the 
shell, even if the rupture is very large ; in fact, unless 
the opening is very large, the escape of steam will be 
so slow that the reduction of pressure will be too grad- 
ual to lead to any such destruction as is frequently 
caused by these explosions. , And I am of the opinion 



64 STEAM-BOILER EXPLOSIONS. 

that all violent explosions occurring when the fire is 
moderate and the steam low, are caused by the explo- 
sive giving-off of steam by water that has been heated 
up to a temperature above that due the pressure. M. 
Magnus and M. Donny have each demonstrated that 
water may be heated in an open vessel to a tempera- 
ture much above its ordinary boiling-point. 

Mr. Bourne, in the eighth edition of his Treatise on 
the Steam-Engine, says (pages 79 and 80) in relation 
to these experiments : " M. Magnus found that water 
well cleared of air may be raised to a temperature of 
105° or 106° C. (222° F.) before boiling. . . . M. 
Donny, however, by freeing the water more carefully 
from air, succeeded in raising it to a temperature of 
135° C. (275° F.), without boiling; but at this tem- 
perature steam was suddenly formed, and a portion of 
the water was suddenly projected from the tube. M. 
Donny concludes, from his experiments, that the nat- 
ural force of cohesion of the particles of water is equal 
to a pressure of about three atmospheres, and to this 
strong cohesive force he attributes the irregular jump- 
ing motion observed in ebullition, and also some of 
those explosions of steam-boilers which heretofore have 
perplexed engineers. It is well known that cases have 
occurred in which an open pan of boiling water has 
exploded with fatal results, and such explosions cannot 
be explained on the usual hypothesis. M. Donny says 
that liquids by boiling lose the greater part of the air 
which they hold in solution, and therefore the molec- 
ular attraction begins to manifest itself in a sensible 
manner. The liquid consequently attains a tempera- 



STEAM-BOILER EXPLOSIONS. 65 

ture considerably above its normal boiling point, which 
determines the appearance of new air bubbles, when 
the liquid separates abruptly, a quantity of vapor 
forms, and the equilibrium is for the moment restored. 
The phenomenon then recurs again with increased vio- 
lence, and an explosion may eventually ensue." 

Professor Miller, of Kings College, London (see his 
" Elements of Chemistry," Part I. page 224), says, 
in relation to this matter : " By long boiling of the 
water the air becomes nearly all expelled: in such a 
case the temperature of the water has been observed 
to rise as high as 360° F. in an open glass vessel, 
which was then shattered with a loud report, by a sud- 
den explosive burst of vapor. In this case the force 
of cohesion retains the particles of the liquid through- 
out the mass in contact with each other, in a species of 
tottering equilibrium ; and when this equilibrium is 
overturned at any one point, the repulsive power of the 
excess of heat stored up in the mass suddenly exerts 
itself, and the explosion is the result of the instanta- 
neous dispersion of the liquid." 

In one instance in my experience, in which I am 
confident now (although at the time it was to me, and 
to other engineers with whom I talked, a perfect mys- 
tery,) that there was such an elevation of the tem- 
perature of the water, the facts are as follows : There 
were eleven boilers in all in the house, plain cylinder 
boilers, thirty inches in diameter, and a little over forty 
feet long. One set, of four of these boilers, were side 
by side, with one furnace under them. They were 
connected below by the feed-pipe, and fed together, and 



65 STEAM-BOILER EXPLOSIONS. 

connected above, at a point rather back of their cen- 
tres, by means of a drum of about the same diameter as 
the boilers, and of a length sufficient to bring its ends 
over the side walls of the setting, so as to serve as a 
means of support to the centres of the boilers. Each 
boiler had an eight-inch nozzle riveted on the top, and 
the drum had four nozzles of the same size. These 
nozzles had flanges, by means of which they were bolted 
together. There was also a connection by means of 
four-inch nozzles and bent copper pipes, just over the 
furnace at the front ends of the boilers, for two safety- 
valves. The expansion and contraction of the drum, 
together with the weight of the boilers, caused the 
nozzles on the drum and on the boilers to leak. There 
were boiler-plate gaskets between the nozzle flanges and 
the boilers, and between the nozzle flanges and the 
drum, and the rivets were " driven" on the outside; 
the leaks were around these gaskets, and they required 
frequent calking. One Saturday night, after the fires 
had been banked up, I closed the valve between the 
drum on this set of boilers and the main steam-pipe, 
took in a good quantity of water, blew off steam, and 
calked these gaskets, leaving the boilers in this condi- 
tion. The heat of the banked-up fire and of the brick- 
work was such that the steam would probably continue 
to rise slowly for ten or twelve hours, when it would 
be at or near the bio wing-off point, — eighty pounds 
per square inch ; and then after standing for some 
time nearly stationary, the pressure would slowly fall, 
so that by the time for starting the fires Monday morn- 
ing it would be about fifteen to thirty pounds. The 



STEAM-BOILER EXPLOSIONS. 67 

boilers stood in this condition till about four o'clock 
Monday morning, perfectly quiet, when the fires were 
drawn forward and cleaned out, but, before they had 
got to burning up at all strong, and when it was sup- 
posed the pressure was about the same as that in the 
main pipe and the other boilers, and probably not over 
forty to fifty pounds per square inch, the starting open 
of the valve at the drum was instantly followed by a 
very severe shock at the front ends of the boilers, and 
the bursting of one of the four-inch copper pipes con- 
necting the boilers at the front ends, from which water 
was thrown. The water then settled down, and all 
was quiet. The pipe burst showed no sign of imper- 
fection in the brazing, and I suppose it would have 
stood a steady pressure of three hundred pounds to 
four hundred pounds per square inch. 

These boilers were nearly new, and of very tough 
one-fourth inch iron, and, taking into account their 
diameter, they were very strong at the front ends, so 
that, although the blow from the water was of tremend- 
ous force, the shells were not broken. The blow appeared 
to be confined to the front ends ; there was no appear- 
ance that the water struck up into the drum or against 
the shells around the big nozzles, which, because of 
the reduction of strength there, caused by the cutting 
out for the nozzles, and the previous strains and leaks 
would have been shown by the opening up of the old 
leaks, but was not the case ; and I am now of the 
opinion that the water just over the fires was heated 
up to a temperature very much above that due the 
pressure, and that the agitation produced by the start- 



68 



STEAM-BOILER EXPLOSIONS. 



ing open of the valve caused it all to give off its steam, 
throwing the water above it with great force against 
the shells of the boilers over the furnace, and that this 
overheating was confined to the water over and very- 
near the fires. 

The water (from Merrimac River) used in these 
boilers was heated by being showered into the top of 
a vertical tank, into which the engines exhausted, so 
that the tallow used for the lubrication of the valves 
and pistons of the engines went into the boilers, and 
it was supposed that the presence of this grease might 
possibly have been the cause of the explosion. But 
an examination, after the explosion, showed the boilers 
to be clean, with the exception of a little sediment at 
the back ends, which showed the presence of the tal- 
low, and a very little greasy coating near the water- 
level. These boilers had to be driven hard to make 
steam for the engines, with a strong draft ; but there 
was never any trouble in the working of the water 
when the fires were strong. That overheating of the 
surfaces of the boilers above the water, or superheated 
steam, was not the cause of the shock, was shown by 
the fact that the water was more than four inches 
above the highest point exposed to the direct action of 
the heat. This was in 1847. 

In 1850, 1 had the charge of two sets of boilers, 
exactly alike ; each set was composed of five boilers, 
thirty-three inches in diameter, and forty-one feet long, 
fed together, a two and one-half inch feed-pipe con- 
necting them at the front end ; the steam connection 
was by means of a drum, of the same diameter as the 






STEAM-BOILER EXPLOSIONS. 69 

boilers, running across the five, with eight-inch nozzles 
on the boilers and drum. The water was got up in 
each set of these boilers one Saturday night, so as to 
show at the upper gauge-cock ; and soon after this the 
fires were banked up, and the steam-valve between one 
set of boilers and the main pipe was closed. From 
the other set, steam was being drawn to two quite 
large dry-rooms. After the boilers had been standing 
in this way for several hours, the pressure on the set 
from which the steam was being drawn, probably very 
nearly as fast as it was made, was found to be nine- 
teen pounds per square inch, and the pressure of the 
other set to be twenty-nine and one-half pounds per 
square inch, by the same gauge, a U mercury gauge. 
The valve connecting the set of boilers in which the 
pressure was twenty-nine and one-half pounds was then 
opened very slowly, but the rise of pressure on the 
main pipe was so sudden as to cause the mercury, 
standing at nineteen pounds pressure, to be thrown to 
very near the top of the tube of the gauge used, which 
was a sixty-pound gauge, with more than six inches 
spare length of tube on the upper end. The mercury 
then fell, and some of it went over into the drain-pipe, 
but just how much could not be known. After a few 
oscillations, the mercury came to rest, and stood at 
twenty-nine pounds strong, — that is, within less than 
one-half pound of the pressure in the boilers where 
the steam was highest. To do this, the steam given 
off by the water in these boilers had to raise the press- 
ure within the other set of boilers, and in the drum 
on them and in the main pipe, which, with its branches, 



70 STEAM-BOILER EXPLOSIONS. 

amounted to nearly one hundred feet of eight-inch pipe, 
one hundred and fifty feet of six inch, forty feet of 
four inch, forty feet of three inch, sixty feet of two 
inch, and over two thousand feet of one inch pipe in 
the two dry-rooms ; and also to raise the temperature 
of a thin film of water (over five hundred square feet) 
in the set where the pressure was lowest ; all the iron 
above the water in this set, its drum and nozzles, and 
the main pipe, over 17° F., showing that a very large 
volume of steam must have been given off by this 
water. 

The water (from Nashua River) used in these boilers 
contained a vegetable matter, and an earthy matter, 
that coated the interior surfaces in such a manner, 
that, when it was let out of them, when the brick-work 
was hot, the coating hardened into a scale ; but if the 
brick-work was cool when the water was let out, it was 
found in the form of a brown, slimy coating over the 
surfaces. 

The method of heating the feed-water was such 
that no grease from the engine went into the boilers, 
and there was never any trouble with the working of 
the water in them when the fires were driven hard, 
with a very strong draft. There was no superheating 
of the steam, or overheating of the iron of the boilers 
above the water. 

In another instance, two tubular boilers, which were 
exactly alike in all respects, set at the same time side 
by side, but having separate furnaces and connections, 
so that one could be used without the other, but which 
had always been run together, were fed one at a time with 



STEAM-BOILER EXPLOSIONS. 71 

water that was heated in the same surface condenser. 
These boilers were run under a pressure of ninety-eight 
pounds per square inch, making steam for an engine 
that was so heavily loaded, that a very slight fall in 
pressure would cause it to take steam full stroke, but 
the circulation of the water was so good in them that 
there was never a sign of trouble with it, even when 
subjected to this trial, with the water showing at 
the top gauge cocks. When these boilers had been 
in use about three years, one of the check valves was 
found to be stuck up with a sort of slimy coating, so 
that in getting it out the spindle was broken. 
The valve was repaired, and nothing peculiar was 
noticed in the working of the boiler when the fires 
were hot, but after they were banked up nights, and 
when the steam, which was used from the two boilers 
for warming the building nights, had been run down 
to about forty pounds per square inch, and when the 
fires were so dead on top that the pressure — as shown 
by a gauge connected with the two boilers — when no 
steam was being drawn from them, rose only at the 
rate of from one eighth to one fourth of a pound per 
minute, this boiler gave unmistakable evidence that the 
water was being heated up to a temperature above that 
due the pressure, and that its temperature was then 
reduced by an explosive generation of steam. The 
shocks produced by these explosions were reported to 
me by the engineer, to be so severe as to shake the 
boiler and its setting. The boiler was very strong and 
no leak was started in it. There were no indications 
of this trouble in the other boiler, which was being 



72 STEAM-BOILER EXPLOSIONS. 

subjected to exactly the same treatment, so far as could 
be seen. The boilers were cleaned out, and very little 
sediment found in them, with no noticeable difference 
in the character of that in the two boilers. But still, 
after the boilers had been standing as above, there 
were the old indications of trouble, only not so heavy ; 
and a second thorough washing of the boiler entirely 
removed the cause of the trouble. 

The method of heating the feed-water in this case, 
was such that no grease from the engine could get 
into it, and there was no superheating of the steam. 
What the effect of opening of a valve so large as to 
have caused much of a reduction of the pressure above 
the water would have been, was not known, the 
branch leading to the warming pipes being so small 
that the opening of its valve would not cause anything 
like a sudden reduction of pressure. 

In each of these three cases, it will be noticed that 
there was no trouble with the water when the boilers 
were being driven hard, and in neither of the two first 
was there the least indication of trouble, such as 
the shocks in the last one, till the reduction of 
pressure caused by the opening of the large valves. 

Very little is apparently known as to the manner in 
which the water becomes so freed from air, or how the 
little particles of solid matter in it are so precipitated 
as to lead to such a heating up. It will be noticed, 
that M. Magnus appears to have been unable to 
free the water used by him of air, so as to raise 
it to a temperature in the open air above about 
222° P., while M. Donny succeeded in reaching a 






STEAM-BOILER EXPLOSIONS. 73 

temperature of 275° F. Professor Miller gives an 
instance of a temperature of 360° F. having been 
reached ; and M. Donny gives cases of explosions of 
open pans of boiling water, " with fatal results." From 
which it appears to me to be probable that the freeing 
of water from air depends very much upon the char- 
acter of the water used, so that the treatment that 
would expel but little of the air from some waters, 
would cause it to become so far expelled from others, 
as to lead to serious results. So far as I am aware, 
very little is known of the effect in this respect, of 
boiling under pressure. It is known that some waters 
may be boiled in a vacuum for some time without 
completely expelling the air ; but, so far as I am aware, 
it is not known that the same water might not have 
its air expelled in a steam boiler working under a 
strong fire and high pressure, the elevation of tem- 
perature of the water, doing with the increase of press- 
ure, what could not be done by the removal of the 
pressure of the atmosphere, at the consequent low 
temperature ; or, that water that has been boiled under 
a high pressure with its consequent elevation of tem- 
perature, may not have its air so far expelled that 
it may be in condition to be raised without boiling by 
a slow fire, under a pressure very much lower, to a 
temperature nearly as great as that to which it had 
before been raised. Another consideration, and one 
which I think may have much to do with the matter 
is this, — that water in a steam-boiler maybe so far 
freed from air, as to be in a condition to have its tem- 
perature raised very much above that due the pressure, 

6 



74 STEAM-BOILER EXPLOSIONS. 

but for the presence of little particles of solid matter 
in it ; and that when the conditions of the water are 
such, that these little atoms of solid matter are all 
precipitated out of the immediate reach of the fire by 
the action of a moderate heat, the continuation of the 
same heat may then raise the temperature of the water, 
either till it gives off steam explosively because its 
molecular attraction is overcome, or till some agitation 
of the water, or an increase of the heat, may throw up 
the little particles of solid matter so that they shall 
become mixed with the overheated water, and so cause 
the excess of heat to be given off in an instant. 

However this may be, or whatever may be the causes 
of the heating up of water in steam-boilers to a tem- 
perature above that due the pressure, I think there 
can be no doubt of the fact, and that it is the cause 
of all the explosions in which the shells of boilers 
are shattered, when the fires and pressure are low ; 
and that in such explosions the water is thrown 
much in the way that it is after repulsion, but accom- 
panied by a greater rise in pressure ; and that so much 
water may be overheated, and to such a degree, that 
so much may be thrown, and with such force, and 
accompanied by such an elevation of pressure, as to 
cause the complete shattering of the shell by the first 
blow. 

That the water is sometimes raised to a very high 
temperature in such explosions, is shown by the fact 
that in several instances so much of it has flashed 
into steam as to leave no sign of water about the ex- 
ploded boiler. Mr. Colburn gives two instances of 



STEAM-BOILER EXPLOSIONS. 75 

• 

this kind, and says in relation to them, — " It has, in- 
deed, been assumed, that in many cases of explosion 
all the water previously contained in the boiler is con- 
verted into steam. Mr. Edward Woods once mentioned, 
at the Institution of Civil Engineers, an instance which 
came under his observation, in 1855, I believe, and 
where, after a locomotive boiler had burst, the whole 
of the water was found to have completely disappeared. 
Mr. Vaughan Pendred, of Dublin, has informed me 
that he observed a similar result after he had exploded 
a small boiler, well supplied with water, for the pur- 
pose of experiment. He had erected a fence of boards 
about the place where the boiler was allowed to burst, 
but on going to the spot immediately afterwards no 
traces of water could be seen." 

Having now considered how boiler explosions are 
caused, we will turn our attention to the matter of 
how they may be prevented ; and, in the consideration 
of the matter of preventing boiler explosions, it is to 
be remembered that the aggregate loss, aside from the 
loss of life, from the use of defective boilers that do 
not explode, is very much greater than the direct loss 
from explosions. The number of boilers that explode 
is but a small percentage of the number built ; but the 
number of boilers in use, in conditions that cannot be 
considered safe, and in which the loss — from the gradual 
destruction of the boilers themselves, from the waste 
of fuel, the injury to engines from the impurities car- 
ried over by the water mechanically mixed with the 
steam, and the loss from the same cause in many dye- 
ing and bleaching operations — is great, is a very large 



76 STEAM-BOILER EXPLOSIONS. 

i 

percentage of the whole number in use. So that the 
saving in dollars and cents resulting from the use of 
means to prevent boiler explosions will be vastly greater 
than the value of the property destroyed by explosions. 
To prevent explosions from low water, boilers should 
be so constructed and set, and have their gauge-cocks 
so placed, that no part of their shells can be over- 
heated when the water is at the lower gauge-cock ; that 
there shall be sufficient steam room and area of water 
level to avoid priming, when the water just shows with 
the steam at the upper gauge-cock ; and that the best 
steaming point shall be with solid water at the middle 
gauge-cock, and dry steam at the upper one. The 
engineer or fireman in charge, should then be held 
responsible for the keeping of the water at this point. 
There should be no dividing the responsibility between 
him and any automatic feeding apparatus whatever. 
The gauge-cocks should be so constructed that they 
can be cleaned out under steam, and always kept clean, 
so that when opened there shall be a clean passage 
through. If the gauge-cocks are connected with the 
boiler by pipes, the boiler end of the pipe must be 
enough lower than the other that water will not re- 
main in the pipe when it is below it in the boiler. If 
glass gauges are used, the above points should be in- 
dicated on a scale near the tube, as to height of 
water; and the connections should be so large and 
direct that the rise and fall of the water in the tube 
shall be so great that the least contraction of the 
area of the lower connection by sediment shall be 
noticed at once; and the connections must be kept 



STEAM-BOILER EXPLOSIONS. 77 

clean. I do not advise reliance upon glass gauges, 
because of the danger connected with the filling up of 
the connections, the coating and loss of transparency 
of the tube, and because of the variation of the level 
of the water in the tubes from causes not easy to under- 
stand. I was once called upon to examine a boiler with 
which there had been a great deal of trouble, which had 
been attributed to priming, where this variation was so 
great as to render the gauge utterly unreliable. The 
water, when the fire was very strong, at times stood 
six inches above its level in the boiler. The guage 
was on the smoke-box cover of a cylindrical tubular 
boiler with the fire under its shell, and the upper con- 
nection ran through the smoke-box to the tube-plate, 
about on a level with the top of the glass tube ; the 
lower connection ran through the smoke-box near the 
shell of the boiler to near the tube-plate, and then 
turned down, following the curvature of the shell to 
near the bottom of the tube-plate, where it entered it. 
When these connections were clean, so that water 
would be blown freely through the lower one, and 
steam as freely through the upper one, and both con- 
nections were opened, — when the fire was strong 
enough to keep up steam for the engine, the water 
would come up to the level of that in the boiler, and 
stand for a moment, and then rise suddenly in the tube 
about an inch, where it would stand for a short time, 
when the operation would be repeated, till, when the 
fire was strong, it would rise as high as before indi- 
cated. Whether this action was alone due to a little 
of an explosive boiling on the bottom of the boiler, to 



78 



STEAM-BOILER EXPLOSIONS. 



the elevation of temperature within the smoke-box, or 
both, I do not know ; but the changing of the lower 
connection, from near the lower part of the tube-plate 
to just above the top row of tubes, cured it, so that 
when the connections were clean, the variation of water 
was not noticeable. I have never since been so well 
assured that I knew where the water in a steam-boiler 
was, by looking at a glass gauge — no matter how well 
the water might appear to be working in the tube — 
but what I wanted also to try the gauge-cocks. 

If from any cause the water gets below the lower 
gauge-cock, the fire should be drawn with the ash-pit 
doors closed and the draft all on, so that the rush of 
cold air over the fire may help to counteract its effect 
upon the boiler ; at the same time if there is an engine 
running, the steam should be gradually shut off from 
it, while some valve that will give a continuous flow of 
steam from the boiler is very gradually opened, and 
this valve must be so regulated that the steam shall 
escape from the boiler just as fast, but no faster, than 
it is made, closing it up fully, when the temperature of 
the brick-work is so low that the pressure does not rise. ' 
The boiler should then stand without the doing of any 
thing to cause the least agitation of the water, and 
allowed to cool down till it can be examined and tested 
before it is used. In relation to this matter the 
Committee of the Franklin Institute say : " If the en- 
gine is at rest, in such a case, it should not be put in 
motion. If it is in motion it should be slackened or 
stopped, the fire-doors opened, and the heat got down. 
The opening of the safety-valve in such a case should 



STEAM-BOILER EXPLOSIONS. 79 

be avoided. The engineer should remember that as 
life is at stake he cannot be too prudent." To call 
attention to the fact of low water, and to help reduce 
'the intensity of the heat in such a case, I advise the 
employment of a suitable low-water safety-plug in the 
crown-sheet, or (if a cylinder boiler with the fire under 
it) in the shell over the fire, and just below where the 
brick-work comes over against the boiler. The reduc- 
tion of temperature, by such an escape of steam into 
a fire, is of very great value as a preventive to the 
burning of the boiler in case of low water. In one 
instance, a large fire-box boiler was saved by its safety- 
plug when its blow-off valve was accidentally opened 
wide, when there was a heavy anthracite coal fire on. 
The reduction of temperature, by the blowing of the 
steam into its furnace, was so great that the fires 
were got out without the starting of a leak in one of 
its two hundred and thirty two-inch tubes. 

There is great misapprehension in the minds of 
many persons regarding the danger of overheating 
the upper part of the shells of boilers, from the fact 
that in many instances boilers have had the upper 
parts of their shells exposed to the action of the gases, 
after they had passed through the flues or tubes, with- 
out serious results. In many instances tubular boilers, 
in which the circulation was so poor that much water 
was thrown up mechanically mixed with the steam, 
have had the consumption of fuel reduced by taking the 
gases, after they had passed through the tubes, over 
the tops of their shells, retaining sufficient heat to 
serve to vaporize the water so thrown up, with the con- 



80 STEAM-BOILER EXPLOSIONS. 

sequent reduction of fuel, but not sufficient heat to 
cause any great heating up of the shell of the boiler, 
or superheating of the steam, even when the shells 
were clean ; and in many instances of this kind I have 
examined, the parts of the shells so exposed have 
been found to be so covered with fine ashes as to be 
pretty well protected from the action of the heat ; and 
I think many more boilers would have had their shells 
broken by the heating up of their tops than have, but 
for this accumulation of fine ashes. And no matter 
how much water may be thrown up mechanically 
mixed with the steam, attempting to vaporize it by 
heating up the top of the shell is an unsafe operation. 

In relation to the heating up of a boiler above the 
water, the Committee of the Franklin Institute say: 
" In a former division of the subject, the Committee 
showed the great danger which is produced in a boiler 
by highly heated metal ; any boiler, therefore, which 
has parts exposed to heat without being in contact 
with water, is essentially defective.' ' 

And the experiments of the Committee demonstrated 
perfectly that the application of heat to the top of the 
shell of a boiler, with a view to the superheating of the 
steam contained in the boiler, is only attended by a 
heating up of the metal of the boiler, and a very little 
of the steam in its upper part. In several instances, 
during these experiments, the steam was superheated 
to a temperature as high as 528° and 533° in the top 
of the boiler, and yet the injection of water at a tem- 
perature below 212° into the steam within the boiler, 
but a few inches below the point where the thermom- 



STEAM-BOILER EXPLOSIONS. 81 

eter indicated the above temperature, did not reduce 
the temperature of the superheated steam, so as to 
cause the thermometer to fall in a single instance. 
So that the vaporization of water thrown up mechani- 
cally mixed with the steam, by taking the hot gases 
over the top of the shell — even though so much water 
is thrown up, that while steam is being drawn from the 
boiler there is no great rise in the temperature of its 
top — is always attended with this danger : that, when- 
ever the demand for steam ceases, the top of the shell 
of the boiler, and a thin film of steam within it, will 
be quickly raised to an unsafe temperature. The vapor- 
ization of this water in the boiler can only be done with 
safety in vertical " fire-tube " boilers, in which the shells 
above the low-water point are not exposed to the action 
of heated gases, and in which the tubes are so small, 
and their length such, that the water can be kept so 
high, without unduly contracting the steam room, that 
there shall be just enough heat left in them to vapor- 
ize the water thrown up ; that is, that the temperature 
of the gases within the tubes at that point, shall never 
be enough above that of the water within the boiler to 
cause a superheating of more than a very few degrees, 
even when the steam is shut into the boiler, when the 
fires are strong. In all other boilers the true remedy 
is to so improve them that the amount of water thrown 
up shall be reduced so low that the steam can be used 
to advantage. While on this matter, it may not be 
out of place to say, that the benefit to be derived 
from superheating, is a very questionable one. It is 
not safe to use superheated steam for warming build- 



82 STEAM-BOILER EXPLOSIONS. 

ings, because of the danger of fire. ■ Probably a very 
large proportion of all fires caused by steam-pipes 
have had their origin in superheated steam. In one in- 
stance of this kind that I investigated, where the fire 
was set over forty feet from the boiler, there were un- 
mistakable evidences that the steam was superheated. 
And whatever theoretical advantages appear to attach 
to the use of superheated steam in a steam engine, in 
practice, the superheating of high pressure steam does 
not pay. The specific heat of steam is so low, that a 
superheating that will cause the serious cutting of 
valves is so far reduced by radiation from the steam- 
chests and cylinder-covers, as to be of very little use 
in the cylinder after expansion commences ; and a 
little condensation on the wearing surfaces of the in- 
terior of a high pressure steam-engine, appears to me 
to be the cheapest way to lubricate them, and, in fact, 
the only way in which an engine of any size can be kept 
from cutting. 

Explosions of properly constructed boilers, by a 
steady increase of pressure, may be prevented by the 
employment of suitable safety-valves and safety-plugs. 
The plugs are to be so constructed, that in case of the 
failure of the safety-valve from any cause, they may be 
broken before the pressure gets so high as to endanger 
the boiler, and placed where they will be acted upon 
by the most intense heat of the fire, so that, in addi- 
tion to the pressure of the steam, they shall have their 
strength reduced by the elevation of temperature, and 
be beyond the reach of accidental or wilful interfer- 
ence ; so placed also that the leak caused by their 



STEAM-BOILER EXPLOSIONS. 83 

breaking shall so far reduce the temperature of the 
fire, as to prevent a greater rise in pressure, even if 
the leak is not observed. The valves, and seats of the 
safety-valves, should always be of composition ; the 
seats should either screw into the cases, or be secured 
by suitable pins ; and the spindles, or wings of the 
valves, should be so much smaller than the holes in 
the seat, as to render it impossible that they shall 
become fixed by the greater expansion of the seat than 
of the case, as mentioned on page twenty-one. 

Explosions from defective materials and construc- 
tion, may be prevented by a proper testing and 
inspection of materials and of boilers ; so that any 
defect in either shall be discovered by the tests, and 
not left to cause the explosion of the boiler. In test- 
ing the plates, great care should be taken to detect 
imperfect welds. Boilers in use should be examined 
very often, by scraping off the soot from any spot, 
having a different appearance from that of the sur- 
rounding surfaces, with a blunt-pointed instrument, 
in order that the first parting off of an imperfect weld 
may be detected. Such blisters, if taken in time, 
may be riveted down so as to make a very much 
better job than can possibly be made by patching. 
Imperfect welds of this kind usually show themselves, 
in new boilers, soon after heavy fires are got up ; but 
in one instance in my experience, where the boilers 
were fed on the bottom over the fire, a weld that had 
stood for over a year, while using hot feed-water, was 
parted by feeding the boilers with cold water. When 
boilers are fed on the bottom over the fire, the feed- 



84 STEAM-BOILER EXPLOSIONS. 



water should always be as hot as possible, not only on 
account of the saving in fuel, but to avoid the dangers 
connected with the sudden reduction of the tem- 
perature of the bottom of the boiler. And it should 
be taken in slowly. Some engineers suppose, that by 
an occasional rush of feed-water into the bottom of a 
boiler over the fire, sediment that has settled there 
may be washed back ; but it is exceedingly doubtful 
whether any substance heavy enough to settle over 
the fire is ever started in this way ; and there can be 
no doubt whatever in relation to the strain thrown 
upon the boiler by the operation. The best place to 
introduce feed-water is through the shell, at some 
distance from the fire, and in such a manner that it 
shall become so mixed with the descending currents 
as to have its temperature raised to very near that of 
the water within the boiler, before it comes in contact 
with the shell of the boiler. And it is advisable on 
all accounts to construct boilers of a quality of iron 
that will give the requisite strength, without having 
to resort to the use of very thick plates. Regarding 
the matter of testing boilers, there is a feeling on the 
part of some, that the testing of a boiler, by forcing- 
water into it with a pump, injures it so that a boiler 
that stands a water-test of a given pressure may have 
its strength so reduced by the operation, as to yield 
immediately after to a steam pressure very much 
lower. It is undoubtedly true, 'that a boiler which 
stands a water-test without a sign of yielding may 
explode soon after at a very much lower pressure, 
because of repulsion, low water, or the overheating 






STEAM-BOILER EXPLOSIONS. 85 

of the water; for a boiler may be so defective in 
relation to adequate provision for the circulation of 
the water, or in relation to the exposure of surface 
above the water-level, as to be utterly unsafe to use, 
and still be strong enough to stand the required water- 
test perfectly ; and such a boiler might explode without 
the previous testing having any thing whatever to do 
with it. And while it is also undoubtedly true that 
many boilers have been injured in testing, by parties 
not qualified to perform the operation, — which is one 
requiring a knowledge of the strength of materials, 
and one that must be performed with much care, — 
it must be borne in mind that testing with water is 
the only safe way to learn that there are not hidden 
defects in the material, that may disclose themselves 
by explosion the first time steam is got up on the 
boiler ; or that there are not such alterations of form, 
as will lead to the destruction of the boiler by the 
constant bending under varying pressures, or that may 
cause leaks that will lead to its destruction by cor- 
rosion, in new boilers ; or that a boiler in use has not 
had its strength so far reduced by corrosion, by un- 
equal expansion, or by alteration of form, as to render 
it unsafe ; and that, when properly performed, it is 
not an operation attended with the least injury to the 
boiler. 

And now we come to the question of what is the 
proper strength of a steam-boiler for any given press- 
ure, and to what water-pressure it should be subjected 
before it is set. I am of the opinion that all boilers, 
intended for working under a pressure of forty pounds 



86 STEAM-BOILER EXPLOSIONS. 

per square inch, or less, should have a calculated 
bursting strength of three hundred and fifty pounds 
per square inch ; and that all boilers intended for a 
working pressure above this, should have this calcu- 
lated bursting strength increased by two and one-half 
times the additional working pressure ; so that a boiler, 
to be worked at a pressure of seventy pounds per 
square inch, should have a calculated bursting strength 
of four hundred and twenty-five pounds per square 
inch ; and one to be worked at a pressure of one hun- 
dred pounds per square inch, should have a bursting 
strength of five hundred pounds per square inch ; and 
that all boilers should be tested, when new, and before 
they leave the shop, with water at a temperature of 
60° to 70°, up to a pressure two-fifths of the calculated 
bursting pressure : — that is, a boiler to be run under a 
pressure of forty pounds per square inch, to one hun- 
dred and forty pounds ; one to be run under seventy 
pounds, to one hundred and seventy pounds ; and one 
to be run under one hundred pounds, to a pressure of 
two hundred pounds per square inch ; and that, at 
these test pressures, there should be no perceptible 
alteration of form, or leak that will not rust up per- 
fectly tight before the boiler is used, without the put- 
ting of any thing whatever into it to cause rusting, or 
filling up of defects in workmanship. The boiler 
should be properly supported before it is filled with 
water, and, as it is filled, the air should all be allowed 
to escape from the highest point of the boiler, so that 
it may be full of water. The effect of every stroke of 
the pump upon the gauge should be observed, and 



STEAM-BOILER EXPLOSIONS. 87 

there should be no difference in the temperature of 
the water in the top and bottom of the boiler. Boilers, 
after being put to work, should be tested once a year, 
and oftener, if it is known that they have been sub- 
jected to an undue strain, or overheating, at a pressure 
three-fourths of that indicated for new boilers. That is, 
an old boiler, working under forty pounds pressure, 
should be tested to one hundred and five pounds ; one 
under seventy pounds pressure, should be tested at 
one hundred and twenty-eight pounds ; and one work- 
ing under one hundred pounds, at one hundred and 
fifty pounds : and this should not be a mere putting 
on of the pressure, and a passing of the boiler because 
nothing breaks, but a thorough examination for alter- 
ation of form, or other indications of weakness ; and if 
any such are found, the boiler should either be strength- 
ened, or the working pressure should be reduced ; and 
if leaks are found, they should be stopped by calking or 
patching ; never by the putting of substances into the 
boiler to fill them up. There are cases where a boiler 
is known to be weak, when a more frequent testing at 
a lower pressure may be advisable, till a change can 
be made without serious loss. In testing old boilers, 
particular care should be taken as to the temperature, 
that their tops are not above that of their bottoms, 
when tested ; they should always be cleaned out after 
being tested. In relation to the testing of boilers, the 
Committee of the Franklin Institute, say, in a form of 
law relating to the matter, submitted with their report, 
" And he (the Inspector,) shall, moreover, provide 
himself with a suitable hydraulic pump, and after 



88 STEAM-BOILER EXPLOSIONS. 



examining into the state and condition of the boiler, 
or boilers, it shall be his duty to test the strength and 
soundness of said boiler, or boilers, by applying to the 
same a hydraulic pressure equal to three times the 
certified pressure which the boilers are to carry in 
steam." Professor Rankine says, in relation to the 
strength of boilers, and the testing of them : " Before 
any boiler is used, its strength ought to be tested by 
means of the pressure of water forced in by pumps. 
The testing pressure should be not less than double the 
working pressure, and not more than one-half the burst- 
ing pressure ; that is to say, as the bursting pressure 
should be six times the working pressure, the testing 
pressure should be between twice and three times the 
working pressure. About tivo and a half times the 
working pressure is a good medium. A pressure 
of water is to be used in testing boilers, because of 
the absence of danger in the event of the boiler giving 
way to it." 

In relation to the great importance of attention to 
the matter of the strength of boilers, Mr. Fairbairn 
says : u It appears to me equally important that we 
should have the same proofs and acknowledged system 
of operations in the construction of boilers, that we 
have in the strength and proportions of ordnance. 
In both cases we have to deal with a powerful and 
dangerous element ; arid I have yet to learn why the 
same security should not be given to the general pub- 
lic as we find so liberally extended to an important 
branch of the public service. In the ordnance de- 
partment at Woolwich, (with which I have been more 






STEAM-BOILER EXPLOSIONS. 89 

or less connected for some years), the utmost care and 
precision are observed in the manufacture of guns ; 
and the proofs are so carefully made under the super- 
intendence of competent officers, as to render every 
gun perfectly safe to the extent of one thousand to 
one thousand two hundred rounds of shot. 

" Boilers and artillery are equally exposed to fracture, 
and it appears to me of little moment whether the one 
is burst by the discharge of gunpowder or the other 
by the elastic force of steam. Surely boilers are 
equally if not more important, as the sacrifice of human 
life appears to me to be much greater in the one case 
than in the other. It would be a matter of paramount 
importance to the public, if men, combining the great- 
est practical skill with the highest scientific attain- 
ments, would give such an undeniable security to 
boilers, as to insure them capable of bearing, under 
the most unfavorable contingencies, at least six times 
their working pressure." 

To prevent explosions caused by scale and sediment, 
steam-boilers should be so constructed, that every part 
of their interior surfaces can be reached for their re- 
moval. And they should not be suffered to accumulate 
so as to exclude the water from the iron ; and to guard 
against overheating caused by the sudden and un- 
suspected accumulation of heavy scale, safety-plugs 
should be put in the parts of the boile^ exposed to the 
most intense heat, of such a character that they shall 
yield, before the elevation of the temperature of the 
boiler is such as to be dangerous. 

The formation of scale and the accumulation of 

7 



90 STEAM-BOILER EXPLOSIONS. 

sediment may be reduced by a judicious system of 
blowing off from parts of the boiler where the water is 
quiet, and where the sediment that settles in still water 
may be reached ; and a good deal of the surface scum 
may be got rid of by the use of pretty large gauge- 
cocks, and, every time the cock at or just below the sur- 
face is opened, letting a quantity escape according to 
the condition of the surface. The blowing off from 
the bottom should be when the boiler is at work, 
and never so much as to expose any part of the 
surface to a temperature above that due the pressure. 
The water should never be let out of a boiler, set in 
brick-work, while there is heat enough in the brick- 
work to harden the slime left on the surfaces into scale. 
In many instances where very hard scale has been 
formed, while the practice of blowing the water out 
under steam was followed, the cooling down of the 
boiler before letting the water out, caused a complete 
change, a slime that could be washed off with the 
hose, being found, instead of a hard scale. Aside 
from all consideration of the danger of explosion, the 
matter of so constructing boilers that every part of 
their interior surfaces can be reached for the removal of 
scale and sediment is of the utmost importance. For 
notwithstanding the fact that these coatings are in 
many instances of such a character, that they are not 
removed fromflrthe surfaces even by a great elevation 
of temperature so as to cause explosions, and also of 
such a character that the water is either not repelled 
from them, or if repelled, their rate of maximum vapor- 
ization is so low that explosion does not follow its 



STEAM-BOILER EXPLOSIONS. 91 

return to them, — still the elevation of temperature of 
the boiler, because of the non-conducting coating, is 
attended by a more or less rapid destruction of the 
boiler, and with a great waste of heat, and of loss of 
power of the boiler. And when the surfaces are so 
covered, it can never be known that so much of it may 
not part off as to lead to the breaking of the boiler, if 
not to an explosion. 

Explosions caused by repulsion may be prevented 
by so constructing boilers, that the circulation of the 
water in them shall be so good, that it shall be brought 
into forcible contact with every part of their surfaces 
exposed to great heat, and to this end they must be so 
constructed that every part of their surfaces can be 
reached for the removal of any sediment or coating that 
interferes with the circulation of the water, so that they 
may be kept clean ; and by the employment of suitable 
safety-plugs in the parts of the boiler from which the 
water is most likely to be repelled, so that in case of 
repulsion the breaking of the plug may cause so grad- 
ual an escape of the steam as to prevent the too sudden 
cooling off of the surfaces, and so save the boiler. 
In case of indications of a repulsive action, nothing 
should be done to cause a sudden rise of pressure, 
or the sudden cooling down of the parts of the boiler 
exposed to the fire ; but the fire should be checked by 
the closing of the damper, and the steam should be 
allowed to escape from the boiler by a steady flow, a 
little faster than made, till the fire and boiler are cooled 
down and the boiler examined. In such a case, the 
opening a little of the blow-off cock at the front end 



92 STEAM-BOILER EXPLOSIONS. 

of the boiler will favor the gradual reduction of the 
temperature of the boiler, and so will be an advantage ; 
but this must be done with great care, and but very 
little, or it will do more harm than good. No feed 
whatever should be taken in till the boiler is cooled 
down. 

And here again we find that the construction of 
boilers, so that the circulation of water within them is 
good, is of very great importance aside from all con- 
sideration of the danger of explosion. For poor cir- 
culation of the water is always attended with a more or 
less rapid destruction of the boiler, and in many in- 
stances this destruction of the parts of the boiler exposed 
to the most intense heat has been very rapid, and yet 
without explosion, because of the presence of a scale 
or coating to which attention has already been called, 
which so far reduces the vaporizing power of the sur- 
faces that the return of the water to them is not fol- 
lowed by an explosive generation of steam. Mr. C. 
Wye Williams, — in his " Elementary Treatise on Com- 
bustion of Coal, and the prevention of Smoke:" John 
Weale, London, 1858, — gives the case of the " Great 
Liverpool," on her first trip to this country in 1842 : 
" The engineer observing the side plates of the furnaces 
continually giving way, some bulging, and others 
cracked and leaking, and some even burnt into holes, — 
although there was always a sufficient height of water 
in the boiler shown by the gauges — supposed there was 
something interfering to keep the water from the plates ; 
and with a view of testing it introduced an inch iron 
pipe from the front into the water space between two 



STEAM-BOILER EXPLOSIONS. 93 

of the furnaces. This at once brought the evil to 
notice; for, although the glass gauge always indicated 
a sufficient height of water, yet nothing issued from 
the pipe but steam as long as the boiler was in full 
action. The overheating was the result of insufficient 
circulation depriving the deep narrow flue spaces of 
an adequate supply of water." When this boiler was 
examined inside, the passages for the descending 
currents were found to be partially filled with scale 
and sediment. 

Poor circulation of water within a boiler is also 
always attended with the throwing up of water me- 
chanically mixed with the steam. Probably there 
are no boilers in use but what throw up water in this 
way ; but in some this is so small as to be of no 
practical importance. Yet in many instances the 
quantity of water thrown up is so large as to be (as 
has before been mentioned) attended with serious 
loss ; and to attempt to remedy such defective boilers, 
by bringing the gases up on their shells, is an oper- 
ation attended with too much danger to be advisable. 
No matter how good the combustion may be, or 
with however little excess of air, or however low the 
temperature of the gases may be when they leave 
the boiler, good results can never be got when the 
circulation of the water is so defective that much of 
it is thrown up mechanically mixed with the steam. 

That the circulation of water may be good, the pas- 
sages for the descending currents should be large and 
clean, and so far protected from the action of the heat, 
as to prevent its interference with the descending cur- 



94 STEAM-BOILER EXPLOSIONS. 

rent. To this end, short cylinder boilers with the fire 
under them should have one end at least protected 
from the heat, and the brick-work on the sides should 
come down so low as to give the water a good start 
down before the action of the heat takes effect upon 
it ; and the tubes or flues of such boilers must be kept 
so far from the shells, and so far apart, as to leave good 
room for these currents. There is no danger but that 
water will rise, but great care is needed in the provision 
for the descending currents. Many boilers now in use 
would give better results, because of the improvement 
in the force of the descending currents, that would be 
made by the removal of quite a percentage of their 
tube surface, or by the covering up of quite a percent- 
age of their shells. 

Designers of boilers have been misled, in regard to 
the amount of surface that could be put into a shell 
with advantage, by the locomotive boiler ; but the 
packing of tubes into a locomotive, the front end of 
which is comparatively cool, and with no heat acting 
upon any part of its shell to interfere with the descend- 
ing currents, cannot be safely followed in boilers which 
have most of the lower parts of their shells exposed to 
the direct action of the fire and heated gases. And 
undoubtedly many locomotives, even, have more tubes 
in them than is for their good. 

Explosions, from a heating up of the water to a 
temperature above that due the pressure, can be pre- 
vented by the use of boilers having a strength in 
accordance with the rule on page eighty-five, and 
by the use of safety-plugs so constructed that their 



STEAM-BOILER EXPLOSIONS. 95 

strength will be so far: reduced as to be broken by a 
very low pressure, before there is such an elevation of 
temperature as to endanger the boiler, — the breaking 
of the safety-plug causing the gradual escape of the 
overheated water, and reduction of the temperature 
of the fire, without any such agitation as to lead to 
the explosive giving off of steam by the overheated 
water. It will also be well in all cases, when a boiler 
has been standing quiet for any length of time, to 
avoid the sudden opening of a valve, so as to cause 
a sudden reduction of pressure and agitation of the 
water ; * and also to avoid taking in feed-water at such 
a time so fast as to cause much agitation in the water, 
or in such quantities as to introduce a great amount 
of air with it. And when the fires have been banked 
up for a considerable length of time, I think it will be 
well, after they are cleaned out, but before they get 
to burning up so as to impart much heat to the boiler, 
to either blow off a little water, let a little steam 
escape, or take in a little feed-water, so as to cause a 
very little agitation of the water, in order that enough 
little particles of solid matter be put in motion, to 
prevent the overheating of the water, before the fire 
gets strong enough to cause the rising of these little 
particles of solid matter, when they have all been pre- 
cipitated far from the furnace. 

But, in my opinion, perfect immunity from the 
danger of explosion, from the overheating of the 



* And, in fact, it is well always to avoid the sudden opening of any 
valve of such a size as to cause a rapid reduction of pressure. 



96 STEAM-BOILER EXPLOSIONS. 

water, can only be secured by the employment of 
boilers having a strength as great as has been before 
indicated, and of such a construction that all their 
surfaces can be reached so that they can be kept 
clean ; and with such provision for the circulation 
of the water, that safety-plugs may be used so weak 
as to be broken by an overheating much below the 
point of danger to the boiler. The doing of these 
things will be attended with such advantages as to 
well repay the doing of them, even without taking 
into consideration the fact of freedom from the danger 
of explosion. 






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